Colin Firth is a "nasty piece of work".

The actor's 'Dorian Gray' co-star Ben Barnes insists the British star is nothing like his polite image as he was such a joker on the set of the movie.

He explained: "Most people think Colin is demure and reserved. I guess he got that image through his films. Truth is he's a nasty piece of work.

"Once I fell asleep on set and he put sticky tape over my mouth and tied my sleeves together. Then he pointed at me and started laughing like a little boy."

The 28-year-old star - who shot to fame playing Prince Caspian in the second 'Chronicles of Narnia' movie - also claimed he feels lucky as he does not attract much attention from the public and is able to go about day-to-day life relatively normally.

He told Austrian website "Fortunately my face isn't quite that well-known yet and I can still walk around unnoticed. Only when I'm at film premieres or at the airport people recognise me. I can still go on the tube or walk around London, though, without anyone knowing who I am, which is great.

"I've only done eight films so far and most people only watched two of them at the most. So far they've only spent about four hours with me."