Colin Firth's latest role was a "physical battle".

The 50-year-old actor stars in 'The King's Speech' as King George VI and found playing the stammering monarch made him so tense he suffered from headaches and trapped nerves, putting him in a "semi-paralysis".

On playing someone so emotionally fragile, he said: "Some part of you goes there. I try to play it as the character would be experiencing it, which is to try not to do it. The sheer physical effort that requires had an effect on my whole body, and while shooting 'The King's Speech' I suffered from headaches.

"Playing the role would put my left arm to sleep. I must have been tensing, particularly if I had long speeches. I must have been locking someone, pinching a nerve, because I couldn't use it properly. It was a semi-paralysis that would last for three or four days.

"So I found myself in a physical battle."

Colin also found after spending so long portraying someone with a stammer, he found the vocal tic surfacing when he spoke away from filming.

He added: "Even now I find myself stammering. Every time I talk about it, I am in danger of losing my flow."