THE Foreign Office has said it is "working urgently to verify" a video purporting to show the beheading of British aid worker David Haines.

The 44-year-old was thought to be being held by Islamic militants in Syria after being taken hostage in March last year.

A video was released tonight which appears to show Mr Haines talking to the camera before being murdered.

A spokeswoman for the Foreign Office said: "We are aware of the video and are working urgently to verify the contents."

The news came hours after the family of Mr Haines issued a plea to his captors to contact them.

The graphic video begins with a clip from David Cameron and then features a man appearing to be Mr Haines dressed in orange overalls and kneeling down in front of a man holding a knife.

The victim looks into the camera and says: " My name is David Cawthorne Haines. I would like to delcare that I hold you David Cameron entirely responsible for my execution.

"You entered voluntarily into a coalition with the United States against the Islamic State just as your predecessor Tony Blair did, following a trend against our British prime ministers who can't find the courage to say no to the Americans.

"Unfortunately it is we the British public that in the end will pay the price for our Parliament's selfish decisions."

The militant, who appears to have a British accent, is recorded as saying: " This British man has to the pay the price for your promise, Cameron, to arm the Peshmerga against the Islamic State.

"Your evil alliance with America which continues to strike the Muslims of Iraq and most recently bombed the Haditha Dam will only accelerate your destruction and playing the role of the obedient lapdog Cameron will only drag you and your people into another bloody and unwinnable war", the militant continues.

The video then appears to show the man take a knife to Mr Haines' throat, before the victim's dead body is shown.