Josh Hartnett is set to sue a British tabloid over allegations that he was caught on camera romping with an unknown female.

The actor reportedly intends to take the Daily Mirror to court for suggesting his 'sexual dalliance' was captured on CCTV after he was warned by security at the Soho Hotel in London to keep it in his trousers.

"It's incredible the stories they (the British newspapers) come out with," he tells GMTV.

"In the States at least they have to make a call to a representative and try to make a reality out of the situation. Over here (in Britain) they just make things up.”

"(The paper said) there was a rumour about a video. But how can you have a rumour about a video? It would be on the Internet (by) now."

Josh is now after an apology and damages from the newspaper.

The allegations are "not only untrue but a complete fabrication.... defamatory and unsubstantiated," his legal reps claim.

The actor got swamped by fans recently as he left rehearsals for new West End show Rain Man...