UK jihadists: British Muslim 'willing to join Islamic State'
15 August 2014 Last updated at 20:24 BST
Hundreds of British extremists who have travelled to Iraq and Syria could return to the UK if jihadist groups start to lose the battles they are involved in, the Metropolitan Police commissioner has warned.
The BBC has spoken to one British Muslim who says he is willing to join Islamic State fighters, believing it is his religious duty.
Ed Thomas reports.