Web blocking in the United Kingdom
The precise number of websites blocked in the United Kingdom is unknown. Blocking techniques vary from one Internet service provider (ISP) to another with some sites or specific URLs blocked by some ISPs and not others. Websites and services are blocked using a combination of data feeds from private content-control technology companies, government agencies, NGOs, court orders in conjunction with the service administrators who may or may not have the power to unblock, additionally block, appeal or recategorise blocked content.

Overview 
There are a number of different web blocking programmes in the UK. The high-profile default ISP filters and IWF filters have been referred to as a "pornwall", "porn filter", "Hadrian's Firewall", "Great Firewall of Britain"  and the "Great Firewall of Cameron". However the programmes are usually referred to interchangeable or individually rather than collectively.

Inciting racial hatred was removed from the IWF's remit on the setting up of a police website for the purpose in April 2011.

The technical measures used to block sites include DNS hijacking, DNS blocking, IP address blocking, and Deep packet inspection, making consistent verification problematic. One known method is ISP scraping DNS of domains subject to blocking orders to produce a list of IPs to block.

The Open Rights Group has proposed adding the new HTTP status code '451' to help streamline and add transparency to the process of determining when a site is blocked.

Active programmes

Copyright

Court-ordered blocks
It is an established procedure in the UK for rights-holders to use 'Section 97' court orders to require ISPs to block copyright-infringing sites. For instance, court orders obtained by the BPI in October 2013 resulted in the blocking of 21 file-sharing sites including FilesTube and Torrentz. There is a private agreement in principle between leading ISPs and rights holders, made with encouragement from government, to quickly restrict access to websites when presented with court orders. The court orders are not made public and "overblocking" is sometimes reported, such as the accidental blocking of the Radio Times, Crystal Palace F.C., Taylor Swift and over 100 other websites in August 2013.

The practice originated as a result of a court order applied against an incidence of copyright infringement that was taken out by the Motion Picture Association in December 2010 at the request of Hollywood studios. The Association applied for an injunction to block access to NewzBin2, a site which provided a search service for UseNet content, indexing downloads of copyrighted content including movies and other material shared without permission. The application was lodged against BT, the largest Internet service provider in the United Kingdom with around six million customers. It required BT to use Cleanfeed to block its customers' access to the site. In July 2011 the High Court of Justice granted the injunction and in October 2011 BT was ordered to block access to the website within fourteen days, the first ruling of its kind under UK copyright law. The precedent set was described by the Open Rights Group as "dangerous". BT did not appeal against the ruling and put the required block in place on 2 November 2011. Subsequent attempts to access the site from a BT IP address were met with the message "Error - site blocked". Newzbin released client software  to circumvent the BT blocking, using encryption and the Tor network.
Newzbin claimed that over 90% of its active UK users had downloaded its workaround software making the BT block ineffective. However, further court orders resulted in Sky blocking access to Newzbin in December 2011 and Virgin Media blocking access to the site in August 2012. On 28 November 2012 Newzbin announced the closure of its indexing service.

Meanwhile, in May 2012 the High Court ordered the blocking of The Pirate Bay by UK ISPs to prevent further copyright infringing movie and music downloads from the website. The blocks were said to be quickly bypassed and a spokesman for The Pirate Party said public interest in the service following the ban had boosted traffic to the party's website.
In December 2012, the British Phonographic Industry (BPI) threatened legal action against The Pirate Party after the party refused demands sent at the end of November to remove their proxy to The Pirate Bay.

In September 2013 an Ofcom survey revealed that 2% of Internet users are responsible for 74% of all copyright-infringing downloads in the UK, and that 29% of all downloads are of content which violates copyright.

In October 2014 the first blocking order against trademark infringing consumer goods was passed against the major UK ISPs by Richemont, Cartier International and Montblanc to block several domains.

ISP Default network blocking
Internet customers in the UK are prohibited from accessing a range of web sites by default, because they have their Internet access filtered by their ISPs. The filtering program has applied to new ISP customers since the end of 2013, and has been extended to existing users on a rolling basis. A voluntary code of practice agreed by all four major ISPs
means that customers have to 'opt out' of the ISP filtering to gain access to the blocked content. However, the complex nature of the active monitoring systems means that users cannot usually opt out of the monitoring and re-routing of their data traffic, something which may render their data security vulnerable. The range of content blocked by ISPs can be varied over time. Categories blocked across the major ISPs include: Dating, Drugs, Alcohol and Tobacco, File sharing, Gambling, Games, Pornography, Nudity, Social networking, Suicide and Self-harm, Weapons and violence, Obscenity, Criminal Skills, Hate, Media Streaming, Fashion and Beauty, Gore, Cyberbullying, Hacking and Web-blocking circumvention tools

History 
The idea for default filtering originated from manifesto commitments concerning "the commercialisation and sexualisation of childhood" given by the parties forming the Cameron–Clegg coalition government in 2010. This was followed by a review (the Bailey Review) and a consultation by the UK Council for Child Internet Safety (UKCCIS). Campaigning by Claire Perry MP and the Daily Mail newspaper resulted in significant public support for the idea of Internet filtering for the purposes of child protection. By 2013 there had already been considerable adoption of in-home filtering, with 43% of homes with children aged 5–15 having filters installed on their family computer. Nevertheless, Prime Minister David Cameron made it clear in July 2013 that his aim was to ensure that by the end of 2013 all ISPs would have a filtering system in place. As a result, three of the Big 4 major ISPs (TalkTalk, Sky and BT) began applying default filtering to new customers in 2013 with the fourth major ISP, Virgin, doing so in February 2014. Default filtering of existing customers was implemented by all four major ISPs during 2014 with the aim of ensuring that the system applied to 95% of all households by the end of the year.

TalkTalk already had content-control software available to comply with government requirements. Their HomeSafe internet filtering system was introduced in May 2011 as an opt-in product and was used for default filtering of new customers from March 2012. HomeSafe was praised by Cameron and is controlled and operated by the Chinese company Huawei. After initial resistance other ISPs had to commission new filtering systems to fulfil Government demands. Some smaller ISPs expressed their reluctance to take part in filtering, citing concerns over costs and civil liberties but the government stated: "We expect the smaller ISPs to follow the lead being set by the larger providers". Cameron said ISPs should choose their own preferred technical solution, but would be monitored to ensure filtering was done correctly. Nevertheless, the ISP Andrews and Arnold does not censor any of its Internet connection all its broadband packages guarantee a 12-month notice should it start to censor any of its traffic.

In July 2014 Ofcom released a report into filter implementation and effectiveness across the fixed-line ISPs. At that point the Big 4 major fixed-line ISPs comprised 93% of the broadband market. They were all mandating filters be enabled as default for new customers, but overall take-up figures were low, with BT (5%), Sky (8%) and Virgin (4%). The figure was higher for TalkTalk (36%) as there had already been significant take-up of its system during the preceding three years. The industry average was 13%. In January 2015 Sky went further, blocking all material deemed unsuitable for children under the age of 13 for any of its five million customers who had not already opted out. In the same month Talk Talk announced that customers who had not chosen whether to activate the company's filtering system would have to opt out if they wished it to be turned off. In January 2016 Sky began sending all new and existing customers an email asking if they want to turn the filter on. Those customers who ignore the email have the filter turned on automatically.

Legal status 

The initial legal status of ISP web blocking was voluntary, although there were a number of attempts to introduce legislation to move it onto a mandatory footing. David Cameron first announced such legislation in July 2013 but default filtering was rejected at the September 2013 conference of the Liberal Democrats (the Coalition Government's minor partner) and no Government legislation to this effect occurred during the 2010-15 Parliament.

Prior to the 2015 2015 United Kingdom general election both the opposition Labour Party and the governing Conservative Party said that, if elected, they would legislate on the issue. Labour said that it would introduce mandatory filters based on BBFC ratings if it believed that voluntary filtering by ISPs had failed. The Conservatives said that they would give an independent regulator such as ATVOD the legal power to compel internet service providers to block sites which failed to include effective age verification. The Digital Economy Act 2017 placed the requirement for ISP filtering into law and introduced a requirement for ISPs to block pornographic sites with inadequate age verification.

Proposals to create a single digital market for European Union (EU) member states include rules for net neutrality. These rules require that all internet traffic has to be treated equally, without blocking or slowing down certain data. Net neutrality guidelines were announced in August 2016 by the Body of European Regulators of Electronic Communications. It was thought that the rules might restrict the legality of ISP filtering after 2016. In May 2014 the government suggested it would veto European net neutrality legislation due to its conflict with web blocking programmes. In May 2015, a leaked Council of the European Union document on the topic of net neutrality suggested users would have to opt into blocks, rather than opt out as per the current UK government's plans. John Carr of the UK Council for Child Internet Safety said of the proposals: "a major plank of the UK’s approach to online child protection will be destroyed at a stroke". However, the requirement that a UK government adheres to EU rules on net neutrality may disappear at some point in future when the United Kingdom leaves the European Union.

Overblocking and underblocking 

Wide-scale inadvertent "overblocking" has been observed since ISP default filtering was introduced at the end of 2013. Legitimate sites are regularly blocked by the filters of some UK ISPs and mobile operators. In December 2013 the UK Council for Child Internet Safety met with ISPs, charities, representatives from government, the BBFC and mobile phone operators to seek ways to reduce the blocking of educational advice for young people. In January 2014 UKCCIS began constructing a whitelist of the charity-run educational sites for children that had been overblocked. The intention was to provide the list to ISPs to allow unblocking.

Examples of overblocked categories reported include:

 sex education and advice on sexual health
 help with sex and pornography addiction
 support services for rape and domestic abuse
 child protection services
 suicide prevention
 libraries
 parliament, government and politicians
 drug advice

The identification of overblocked sites is made particularly difficult by the fact that ISPs do not provide checking tools to allow website owners to determine whether their site is being blocked. In July 2014 the Open Rights Group launched an independent checking tool blocked.org.uk, a revamp of their mobile blocking site to report details of blocking on different fixed line ISPs and mobile providers. The tool revealed that 19% of 100,000 popularly visited websites were being blocked (with significant variation between ISPs) although the percentage of sites hosting legal pornographic material is thought to be around 4%. 

Significant underblocking has also been discovered, with ISPs failing to block up to 7% of adult sites tested. A study commissioned by the European Commission's Safer Internet Programme which tested parental control tools showed that underblocking for adult content ranged from 5-35%.

Criticism

In favour
Proponents of internet filtering primarily refer to the need to combat the early sexualisation of children. The government believes that "broadband providers should consider automatically blocking sex sites, with individuals being required to opt in to receive them, rather than opt out and use the available computer parental controls." In 2010 communications minister Ed Vaizey was quoted as saying, "This is a very serious matter. I think it is very important that it's the ISPs that come up with solutions to protect children."

Against
The Washington Post described the UK's ISP filtering systems as creating "some of the strictest curbs on pornography in the Western world". There is no public scrutiny of the filtering lists. This creates the potential for them to be expanded to stifle dissent for political ends, as has happened in some other countries. The British Prime Minister of the time David Cameron stated that Internet users will have the option to turn the filters off, but no legislation exists to ensure that option will remain available.

In March 2014, president Diane Duke of the United States-based Free Speech Coalition argued against the censorship rules at a London conference sponsored by Virgin Media. The discussion was titled "Switched on Families: Does the Online World Make Good Things Happen?". The panel included government representatives such as Member of Parliament Claire Perry, members of the press, and supporters of an open Internet such representatives from the UK Council for Child Internet Safety, the Family Online Safety Institute, and Big Brother Watch. A report on the meeting was printed in The Guardian on 5 March 2014. Duke was quoted as saying, "The filters Prime Minister Cameron supports block sexual health sites, they block domestic violence sites, they block gay and lesbian sites, they block information about eating disorders and a lot of information to which it's crucial young people have access. Rather than protect children from things like bullying and online predators, these filters leave children in the dark."

The Open Rights Group has been highly critical of the blocking programmes, especially mobile blocking and ISP default blocking. New Statesman magazine observed that overblocking means “the most vulnerable people in society are the most likely to be cut off from the help they need”.

Categories blocked

In July 2013 the Open Rights Group discovered from the ISPs that a wide range of content categories would be blocked. Blocking has subsequently been detected in all the categories listed by the ISPs apart from 'anorexia and eating disorder websites' and 'esoteric material'. More information was gained following the launch of blocked.org.uk by the Open Rights Group, when TalkTalk gave additional detail about their default blocked categories and BT identified their default filtering level (light).

Mobile Internet blocking
UK mobile phone operators began filtering Internet content in 2004 when Ofcom published a "UK code of practice for the self-regulation of new forms of content on mobiles". This provided a means of classifying mobile Internet content to enable consistency in filtering. All major UK operators now voluntarily filter content by default. Nevertheless, in October 2014 it was reported that Ministers were drafting legislation to compel mobile operators to block access to adult sites unless users prove they are aged 18 or over.

When users try to access blocked content they are redirected to a warning page. This tells them that they are not able to access an 'over 18 status' Internet site and a filtering mechanism has restricted their access. Categories that are listed as blocked include: adult / sexually explicit, chat, criminal skills, drugs, alcohol and tobacco, gambling, hacking, hate, personal and dating, violence, and weapons. Users who are adults may have the block lifted on request.

Guidelines published by the Independent Mobile Classification Body were used by mobile operators to classify sites until the British Board of Film Classification took over responsibility in 2013. Classification determines whether content is suitable for customers under 18 years old. The default assumption is that a user is under 18.

The following content types must be blocked from under 18's:
 Suicide, Self-harm, Pro-Anorexia and eating disorders
 Discriminatory language
 Encouragement of Drug Use
 Repeated / aggressive use of 'cunt'
 Pornography Restrictions
 Violence and Gore restrictions

Significant overblocking of Internet sites by mobile operators is reported, including the blocking of political satire, feminism and gay content. Research by the Open Rights Group highlighted the widespread nature of unjustified site blocking. In 2011 the group set up blocked.org.uk, a website allowing the reporting of sites and services that are 'blocked' on their mobile network. The website received hundreds of reports of the blocking of sites covering blogs, business, internet privacy and internet forums across multiple networks. The Open Rights Group also demonstrated that correcting the erroneous blocking of innocent sites can be difficult. No UK mobile operator provides an on-line tool for identifying blocked websites. The O2 Website status checker was available until the end of 2013 but was suspended in December
after it had been widely used to determine the extent of overblocking by O2. Not only were civil liberties and computing sites being blocked, but also Childline, the NSPCC and the Police. An additional opt-in whitelist service aimed at users under 12 years is provided by O2. The service only allows access to websites on a list of categories deemed suitable for that age group.

Internet Watch Foundation

Introduction 

Between 2004 and 2006, BT Group introduced its Cleanfeed content blocking system technology to implement 'section 97A' orders. BT spokesman Jon Carter described Cleanfeed's function as "to block access to illegal Web sites that are listed by the Internet Watch Foundation", and described it as essentially a server hosting a filter that checked requested URLs for Web sites on the IWF list, and returning an error message of "Web site not found" for positive matches. Cleanfeed is a silent content filtering system, which means that Internet users cannot ascertain whether they are being regulated by Cleanfeed, experiencing connection failures, or if the page really does not exist. The proportion of Internet service providers using Cleanfeed by the beginning of 2006 was 80% and this rose to 95% by the middle of 2008. In February 2009, the Government said that it was looking at ways to cover the final 5%.

According to a small-sample survey conducted in 2008 by Nikolaos Koumartzis, an MA researcher at London College of Communication, the vast majority of UK based Internet users (90.21%) were unaware of the existence of Cleanfeed software. Moreover, nearly two thirds of the participants did not trust British Telecommunications or the IWF to be responsible for a silent censorship system in the UK. A majority would prefer to see a message stating that a given site was blocked and to have access to a form for unblocking a given site.

Cleanfeed originally targeted only alleged child sexual abuse content identified by the Internet Watch Foundation. However, no safeguards exist to stop the secret list of blocked sites being extended to include sites unrelated to child pornography. This had led to criticism of Cleanfeed's lack of transparency which gives it considerable potential for broad censorship. Further, Cleanfeed has been used to block access to copyright-infringing websites after a court order in 2011 required BT to block access to NewzBin2. This has led some to describe Cleanfeed as the most perfectly invisible censorship mechanism ever invented and to liken its powers of censorship to those employed currently by China. There are risks that increasing Internet regulation will lead the Internet to be even more restricted in the future.

Non-BT ISPs now implement the child abuse image content list with their in-house technologies to implement IWF blocking.

IWF/Wikipedia controversy

On 5 December 2008 the IWF system blacklisted a Wikipedia article on the Scorpions album Virgin Killer. A statement by the organisation's spokesman alleged that the album cover, displayed in the article, contained "a potentially illegal indecent image of a child under the age of 18". Users of major ISPs, including Virgin Media, Be/O2/Telefónica, EasyNet/UK Online, Demon and Opal, were unable to access the content, despite the album cover being available unfiltered on other major sites including Amazon.co.uk, and available for sale in the UK. The system also started proxying users, who accessed any Wikipedia article, via a minimal number of servers, which resulted in site administrators having to block them from editing Wikipedia or creating accounts. On 9 December, the IWF removed the article from its blacklist, stating: "IWF's overriding objective is to minimise the availability of indecent images of children on the Internet, however, on this occasion our efforts have had the opposite effect."

Public Wi-Fi 
The vast majority of the Internet access provided by Wi-Fi systems in public places in the UK is filtered with many sites being blocked. The filtering is done voluntarily by the six largest providers of public Wi-Fi: Arqiva, BT, Sky, Nomad Digital, Virgin and O2, who together are responsible for 90% public Wi-Fi. The filtering was introduced as a result of an agreement put in place in November 2013 between the Government and the Wi-Fi providers. Pressure from the Government and the UK Council for Child Internet Safety had already led Virgin and O2 to install filtering on the Wi-Fi systems on the London Underground and McDonald's restaurants,
but half of all public Wi-Fi networks remained unfiltered in September 2013.

"Overblocking" is a problem reported with public Wi-Fi filters. Research in September 2013 indicated that poorly programmed filters blocked sites when a prohibited tag appeared coincidentally within an unrelated word. Religious sites were blocked by nearly half of public Wi-Fi filters and sex education sites were blocked by one third. In November 2013, there were complaints about the blocking of Gay websites that were not related to sex or nudity on the public Wi-Fi provided by train operating companies. The filtering was done by third party organisations and these were criticised for being both unidentified and unaccountable. Such blocking may breach the Equality Act 2010. The government arranged for the UK Council for Child Internet Safety to investigate whether filters were blocking advice to young people in areas such as sex education.

Libraries and educational institutions
Many libraries in the UK such as the British Library and local authority public libraries apply filters to Internet access. According to research conducted by the Radical Librarians Collective, at least 98% of public libraries apply filters; including categories such as "LGBT interest", "abortion" and "questionable". Some public libraries block Payday loan websites and Lambeth Council has called for other public Wi-fi providers to block these sites too.

The majority of schools and colleges use filters to block access to sites which contain adult material, gambling and sites which contain malware.  YouTube, Facebook and Twitter are often filtered by schools.  Some universities also block access to sites containing a variety of material.  Many students often use proxy servers to bypass this. Schools often censor pupils' Internet access in order to offer some protection against various perceived threats such as cyber-bullying and the perceived risk of grooming by paedophiles; as well as to maintain pupil attention during IT lessons.  Examples of overblocking exist in the school context.  For instance, in February 2014 the website of the Yes Scotland pro-independence campaign was blocked in a Glasgow school while the rival Better Together pro-union website was not blocked.

Planned programmes

Extremism

The Counter Terrorism Internet Referral Unit (CTIRU), which was set up in 2010 by the Association of Chief Police Officers and run by the Metropolitan Police Service, maintains a list of sites and content that in their opinion incites or glorifies terrorist acts under Section 3 of the Terrorism Act 2006. This list is passed to the public estate institutions so that access to the sites can be blocked. ISPs BT, Sky, TalkTalk and Virgin Media incorporate the CTIRU block list into their filters. The CTIRU also issues removal requests if the Internet content is hosted in the UK. The UK is the only country in the world with such a unit.Home Office proposals in 2006 requiring ISPs to block access to articles "glorifying terrorism" were rejected and the government opted for a takedown approach at that time. However, in December 2013 the Prime Minister's extremism task force proposed that where such material is hosted overseas, ISPs should block the websites, and David Cameron gave orders that the CTIRU list be extended to UK ISPs. The UK government has defined extremism as: "Vocal or active opposition to fundamental British values, including democracy, the rule of law, individual liberty and mutual respect and tolerance of different faiths and beliefs."

This approach to web blocking has been criticised for being extra-parliamentary and extrajudicial and for being a proactive process where authorities actively seek out material to ban. Additionally, concerns have been expressed by ISPs and freedom of speech advocates that these measures could lead to the censorship of content that is “extremist” but not illegal. Indeed, the United Kingdom security minister James Brokenshire said in March 2014 that the government should also deal with material "that may not be illegal but certainly is unsavoury and may not be the sort of material that people would want to see or receive".

Unimplemented proposals

Social media and communications

Private members' bills
A private members bill requiring ISPs, mobile phone operators and equipment manufacturers to filter adult content was introduced into the House of Lords in May 2012 by Baroness Howe of Idlicote. The Online Safety Bill was criticised for its potential to block any service that appears to provide adult material unless it is on an Ofcom-approved list. The original bill did not succeed due to a lack of Government support. It was re-introduced in May 2015 and failed a second time.

In September 2014 as a proposed addition to UK legislation against revenge porn, Geraint Davies MP introduced a private member's bill mandating devices that can access the Internet be filtered by default at the threat of fining non-compliant manufacturers.

After the bill's first reading there was no debate and the bill made no further progress.

Although these legislative approaches were unsuccessful as private member' bills, their measures may appear in a future Government Communications Bill.

Online Harms White Paper 

In 2019, the UK government published its Online Harms White Paper, which covers many of the "online harms" discussed above.
The government's new proposed solution to these problems is to introduce a wide-ranging regime of Internet regulation in the United Kingdom, enforcing codes of practice on Internet companies, which would be subject to a statutory duty of care, and the threat of punishment or blocking if the codes are not complied with.

Technologies

By ISP 
A service provider will integrate some or all its feeds into a single filtering device or stack, sometimes in conjunction with an upstream provider performing additional filtering. The following content-control technologies have been confirmed to be used to implement all types of web blocking (includes virtual operators):

Rulespace and O2 are the only known services with a public categorisation and blocking check tool.

By feed type

Circumvention 

Site blocks can be circumvented using method trivial through to complex such as use of Tor, VPNs, site specific and general web proxies, and other circumvention techniques.

Child abuse image content list 
Due to the proxy server implementation of the IWF's child abuse image content list (formally Cleanfeed) system, websites that filter users by IP address, such as wikis and file lockers, will be significantly broken, even if only a tiny proportion of its content is flagged.

Copyright 
In response to the increasing number of file sharing related blocks, a number of proxy aggregator sites, e.g. torrentproxies.com, have become popular. In addition to the following, proxy sites designed to circumvent blocks have been secretly blocked by ISPs, driving users to proxy comparison sites. The Pirate Bay created a version of Tor branded as the PirateBrowser specifically to encourage anonymity and circumvention of these blocks. On August 5, 2014, City of London Police Intellectual Property Crime Unit arrested a 20-year-old man in Nottingham on suspicion of operating a proxy server that allowed internet users to bypass blocks on many popular sites.

ISP default network blocking
Downloadable software enabling web browsers to bypass the ISP filtering began appearing in December 2013, and in 2014 versions began appearing for mobile Internet platforms.