New cases: The decision not to prosecute Lord Janner over historic abuse claims has prompted 30 more alleged victims to come forward . A dossier on Lord Janner is among 114 files on child sex abuse that has vanished from the Home Office, it was revealed today. The 1986 Janner file is mentioned in an investigation into an alleged government cover up but its contents remain a mystery. The Home Office has refused to comment on the dossier, which could potentially conceal the name of a second person, it is alleged. Last year NSPCC boss Peter Wanless led a review of Home Office files from 1979 to 1999 and concluded it would be 'impossible' to unearth this and the other 113 missing files. According to the Daily Mirror the paper, titled ‘Greville Janner MP [redacted] re evidence in child abuse cases’ is listed as ‘not found’ and ‘presumed transferred to the MoJ [Ministry of Justice] but not located’. It came as it emerged up to 30 people have now reportedly told police they were abused by Lord Janner, with more coming forward since it was announced he will not be charged with child sex offences. Publicity surrounding the case has encouraged a new wave of alleged victims to come forward, The Times said last night. The news came as Britain’s law chief spoke out publicly for the first time since she ruled the former MP would not face a trial because of his dementia. Yesterday the Director of Public Prosecutions Alison Saunders dared her critics to challenge her in court, and said she is not afraid to see the controversial move tested by a High Court judge. In an appearance on Newsnight she said her decision on Lord Janner was correct when asked if she would not change her mind. She said: 'No. I’ve considered the decision very carefully. I mean this wasn’t an easy decision to make and I am very aware of the disappointment and frustration that some people will feel around the decision and I feel frustrated that we cannot and haven’t been able to prosecute it. Scroll down for video . The news came as Alison Saunders, the new Director of Public Prosecutions, has dared her critics to challenge her in court after she decided Lord Janner could not face trial because of his Alzheimer's . An explosive dossier compiled by MP Geoffrey Dickens is believed to be among 114 files known to have been lost or destroyed by the Home Office. In 1983 the Tory MP for Huddersfield West said he had eight names of 'really important, public figures' who unless they were arrested he would ‘expose in Parliament’. Based on his descriptions, these are thought to include MPs, civil servants, a diplomat and even a Buckingham Palace official. Some had links to the Paedophile Information Exchange, who wanted sex with children legalised, he said. Dickens handed his '40-page dossier' to the then Home Secretary Leon Brittan, which set out allegations of a paedophile circle ‘operating and networking within and around’ the Westminster elite. Another copy was kept by Mr Dickens' wife and another was allegedly handed to the then Director of Public Prosecutions, Sir Thomas Hetherington and then the police. All the copies vanished and nothing came of the investigations but now the Dickens dossier is central to allegations that there was a high level cover-up to protect those in power. 'But I have to apply the code for Crown Prosecutors and that means I look at the evidence first: I was satisfied there was a realistic prospect of conviction. 'And then I look at the public interest, which means taking into account Lord Janner’s medical condition and his dementia, which is so severe that in my view he would not be able to stand trial. Not just in my view, but more importantly, in the view of the medical experts and we had four medical experts where I was able to take their advice.’ She also brushed aside calls for her resignation, insisting that ‘making the right decision is not a resigning issue’. In an interview with London’s Evening Standard yesterday, the DPP dismissed claims that she was part of an Establishment cover-up. She admitted that she has paid a ‘heavy price’ for the decision, but said: ‘If somebody wants to challenge my decision I’m not afraid. 'The proper way to challenge it is through the right to review or a judicial review. I’m confident that if they want to do that my decision will stand up.’ Mrs Saunders said she was right to avoid the ‘easy option’ of sending the case to court for a judge to throw out. Last week Leicestershire Police said they were considering a legal challenge, most likely a High Court judicial review. Victims also have the right to review charging decisions, but so far no one has come forward with a request.
Publicity surrounding case has prompted 30 people to contact police .
Revealed dossier on Lord Janner was among files lost by Home Office .
DPP Alison Saunders has told critics to challenge her ruling in court .
Also said that her decision is 'the right one' and will not change .