Colin Firth believes starring in 'Mamma Mia' is one of the "best things" he has ever done.

The actor has won the Best Actor awards at both the Golden Globes and the BAFTAs for his role as King George IV in 'The King's Speech'.

In an interview with America's CBS show '60 Minutes' he explained while people expect him to be ashamed of his all-singing, all-dancing role in the musical 'Mamma Mia', he counts it as one of his biggest achievements.

He said: "I think it is one of the best things I have ever done. People expect me to be apologetic about it but I’m not.

"Right now I would say there’s three things of which I am most proud, 'A Single Man', 'The King’s Speech' and 'Mamma Mia'."

The 50-year-old star also joked that it didn't take much persuasion for him to appear as Harry Bright in 'Mamma Mia' because he is a "drag queen" with "no shame".

Firth added: "That may be the reason I did it. I have no shame. I am such a drag queen, it’s one of my primary driving forces in life.

"You cannot dangle a spandex suit and mascara in front of me and not expect me to go weak at the knees."