Britain's Colin Firth won his first Oscar on Sunday for playing a stammering monarch in "The King's Speech", crowning a virtual clean sweep of the movie awards season.

The best actor victory was expected for the 50-year-old veteran of the screen and stage after his acclaimed portrayal of reluctant wartime King George VI, struggling to overcome a crippling speech impediment.

"I have a feeling my career has just peaked," Firth deadpanned as he accepted his Academy Award. He also won Golden Globe, BAFTA and Screen Actors Guild trophies for the role.

"I am experiencing stirrings somewhere in the upper abdominals which are threatening to form themselves into dance moves, which joyous as they may be for me, would be extremely problematic if they make it to my legs before I get off stage," he added.

Firth was Oscar-nominated last year for his role as a closeted gay professor in the drama "A Single Man." He becomes the sixth best actor Oscar winner in 10 years to win for playing a real-life character.

Before his dramatic roles in "The King's Speech" and "A Single Man," Firth had been best known for playing handsome but buttoned-up English men in romantic comedies such as "Love Actually" and "Bridget Jones's Diary."

Speaking backstage, Firth said the royal movie, set in the 1930s, had resonated with audiences on a personal level.

"What has struck me is the emotional response to it, which seems to have been very, very personal and quite diverse," Firth told reporters.

But he said he was not in favor of the U.S. release of a cleaned-up PG-13 version of the movie, which removes a scene in which the shy king curses in frustration.

"I don't support it, because I think the film has an integrity where it stands. I think that scene belongs where it is, " Firth said.

"In the context of this film, it could not be more edifying, more appropriate," he added. "It's about a man trying to free himself through the use of forbidden words...so, I think the film should stand as it is."

On Sunday he thanked his Italian wife Livia for putting up with his "fleeting delusions of royalty" while filming.

He also said he was planning to cook a lot after months of red carpets and award shows. "I don't think I'm particularly good at it (but) I do think that is a good way to decompress."

Firth's rivals on Sunday were previous Oscar winners Javier Bardem for "Biutiful" and Jeff Bridges for "True Grit"; Jesse Eisenberg for "The Social Network"; and Oscars host James Franco for "127 Hours."