Foreign Secretary Philip Hammond has said he expects the response to Islamic State to be a "long struggle against a poisonous ideology".
He said the military dimension of the conflict was just one part of the counter-attack, which he said is also financial and ideological.
ITV News' International Affairs Editor Rageh Omaar began by asking him whether Parliament would be consulted in advance of any military action:
I've been told at the Nato summit that the intelligence services know exactly who 'Jihadi John' is - or at least are 99.9% certain.
The British aid worker being held by Islamic State is David Haines, a 44-year-old father-of-two from Perth, Scotland.
In a video statement which claims to record his final words US hostage and journalist Steven Sotloff blames US foreign policy for his death.