Emergency vehicle equipment in the United Kingdom

Emergency vehicle equipment is used in the United Kingdom to indicate urgent journeys by an emergency service. This usage is colloquially known as Blues and twos which refers to the blue lights and the two-tone siren once commonplace (although most sirens now have a range of tones like Wail, Yelp and Phaser). A call-out requiring the use of lights and sirens is often colloquially known as a blue light run.
Permitted use.
In the United Kingdom, the use of blue lights is regulated by the Road Vehicles Lighting Regulations 1989, and sirens by the Road Vehicles Construction and Use Regulations 1986, both as amended by various other pieces of legislation (see right). The 1989 restrictions state that no vehicle, other than an emergency vehicle, shall be fitted with a "blue warning beacon or special warning lamp", or a device which resembles a blue warning beacon or a special warning lamp, whether it works or not.
Each of the emergency services listed above has different policies regarding the use of blue lights and sirens. Most require the driver to be trained to a particular standard in response driving, but currently, no national standard exists. Provision exists for a national standard to be required in order to utilise speed limit exemptions, but this has not been brought into force.
Road traffic exemptions.
In the UK, vehicles used for certain purposes may have exemptions from some road traffic regulations whilst responding to an emergency. Merely being authorised to use blue lights and sirens does not of itself grant exemptions from road traffic law. These exemptions apply whether or not blue lights and/or sirens are being used, although it is mainly desirable: