Colin Firth has confessed that he had "initial" fears over starring in the big screen adaptation of John Le Carré’s Tinker, Tailor, Soldier, Spy.

The Oscar-winning actor admitted that he felt nervous about his first days on set in his role as Bill Haydon in the Tomas Alfredson thriller.

In an interview with PA, The King's Speech star said: "There's an initial moment when you walk on the set and think, 'Oh, I might be out of my league'."

Firth stars alongside John Hurt, Gary Oldman, Mark Strong, Tom Hardy, Benedict Cumberbatch and Toby Jones in the film.

He said it was "a thrill to be surrounded by brilliant people" because it "lifts your own game".

However, he added: "I don't think any actor is so selfless to only luxuriate in ensemble work, but I was absolutely up for it."

Colin said the idea of bringing the book, which he hadn't read before getting the role, to the big screen "seemed very cool to me".