The Channel programme is part of the government’s wider anti-terrorism strategy and was set up following the 7/7 attacks in 2005 to identify people vulnerable to extremism.

It is then supposed to work with schools, social services, the police and local councils to keep them away from danger.

Terrorism experts said online propaganda meant police were finding young people exposed to extremist ideas at younger and younger ages.

The controversial legal obligation to flag up potential cases, known as the Prevent duty, has also led to a huge increase in young people being referred. One social worker from east London told The Telegraph that she was now regularly having to involve the police as rebellious and often troubled teens parroted Islamist ideas they had seen on the internet.

What is Isil? An Islamist extremist group controlling territory in Syria and Iraq

What is it called? In the West, the group is usually known as Isil (Islamic State of Iraq and the Levant) or Isis (Islamic State of Iraq and Syria). The militants said they wanted to simply be called Islamic State in recognition of the self-declared caliphate

What about ‘Daesh’? Daesh is an abbreviation Dawlat al-Islamiyah f’al-Iraq wa al-Sham, and is the derogatory name used by many Muslims for Isil. Following the Paris attacks, the French government is now using this term

What are its aims? A worldwide Islamic caliphate – a religious government without borders

What terror attacks has it carried out? Isil has claimed responsibility for the Paris attacks of 13 November 2015, the explosion of a plane travelling from Egypt to Russia, and the individual killings of Western hostages, including James Foley and Alan Henning

Where is it based? Isil’s HQ is in the city of Raqqa, Syria