By Chris Ship: Deputy Political Editor
After meeting MI5 and MI6 this afternoon, the Prime Minister again repeated there would be no British combat boots on the ground and no British air strikes.
But at Downing Street they assess that Britain is still a threat, irrespective of what we do militarily in Iraq.
Their particular concern is the 500 or so Britons who have gone out to join these fighters and fight for extremists, amid concern they may well find their way back to the UK and bring that terrorism with them.
There was also an interesting intervention today from Scotland Yard, who've urged people not to share this video online and on social media - and warned anyone that who does use it to incite extremism faces prosecution.
A British family have told ITV News of their devastation after discovering a close relative is fighting with the Islamic State in Iraq.
A French journalist who was held hostage with James Foley in Syria has told ITV News it was "devastating" to see his murder.