Colin Firth was anxious about dropping his trousers in 'Gambit'.

The 52-year-old actor strolls through the Savoy Hotel wearing nothing but a shirt in the new Coen Brothers' scripted comedy, and he was embarrassed about his un-gentlemanly attire and exposing his legs on camera.

Speaking at the world premiere of 'Gambit' in London's Leicester Square last night (07.11.12), Colin told BANG Showbiz: ''I did have a bit of leg anxiety at the time. It's one thing to basically drop everything, but just the trousers ... It's just not a look that's recommended for a gentleman - brogues, socks up to the knees, underpants!''

The Hollywood heartthrob had a blast filming with Cameron Diaz, and says she always brought her sense of humour to the set, even during his most nerve-wrecking scenes.

He added: ''It's been fabulous she's the best at what she does. There were plenty of funny moments on set. [I mean], If you have to walk with your trousers off through the lobby of the Savoy Hotel...''

'Harry Potter' star Alan Rickman takes things one step further with a sequence filmed entirely in the buff, but he confessed he was more confident about shedding his clothes than his co-star.

He explained: ''You just have to get on with it, there's no choice, 'OK, right here we go!' ''

The stars were joined by director Michael Hoffman and co-star Tom Courtenay on the red carpet.