On an August bank holiday in 2014, Shiraz Maher at the International Centre for Study of Radicalisation at Kings College London received an email sent by a disillusioned British jihadist from Syria.
"We came to fight the regime and instead we are involved in gang warfare. It's not what we came for but if we go back to Britain we will go to jail. Right now we are being forced to fight - what option do we have?"
The man in his twenties claimed to represent dozens of other jihadists' desperate to return to the UK but fearing long prison sentences.
Gordon Corera explores the British government's response to managing returnees. In the last two years Britain has brought in temporary exclusion orders and is able to confiscate passports to prevent people preparing to travel to Syria.
France has gone one step further - since the Paris attacks in November police has placed over 400 citizens under house arrest and can strip French born dual nationals of citizenship. Denmark and Germany have taken a different approach and instead try to rehabilitate rather than imprison; helping young men and women get jobs, housing and education.
The Home Office estimates that around 800 British nationals have travelled to Syria since the start of the conflict and that around half of those have returned, though experts say these are conservative figures. What's the best way to deal with this growing threat, particularly when returnees are responsible for attacks such as those in Paris last November?
Gordon Corera speaks with Shiraz Maher, Rashad Ali of the Institute of Strategic Dialogue, solicitor Gareth Peirce, Hanif Qadir of the Active Change Foundation and counter-terrorism officer DAC Helen Ball. We also hear from a returnee.
Producer: Caitlin Smith.