David Cameron has announced new laws to crack down on terror suspects as he warned that extremism in Iraq and Syria poses a greater danger to Britain than al Qaida.

As the terrorist threat to the UK was raised from substantial to severe, the Prime Minister said legislation would be introduced so it was easier to seize jihadists' passports.

"What we are facing in Iraq now with Isil (Islamic State) is a greater threat to our security than we have seen before," he told a press conference in Downing Street.