For more than 20 years, Colin Firth has been the movie industry's go-to, buttoned-up English man.

But audiences have never seen him quite as emotionally (and physically) naked beneath that characteristic quiet restraint as in fashion designer Tom Ford's directing debut, A Single Man.

Firth, 49, whose past roles include the awkward but alluring Mark Darcy in Bridget Jones's Diary and the diffident Jamie Bennett in Love Actually, turns in what critics say is an Oscar-worthy role of a lifetime as a gay, 1960s British professor grieving over the loss of his lover.

A Single Man, which has already brought Firth a best actor award at the Venice film festival, opens in limited release in the United States on Friday.

For Firth, the role of George making his way through the last day of a broken-hearted life he plans to end by suicide, was an embarrassment of riches -- and one that despite more than two decades in show business has rarely come his way.

Despite this man's rather contained exterior, he experiences despair, lust, frivolity, anger, fear, wistfulness, regret, tenderness -- the list of emotions is extraordinary, the actor told Reuters.

I can't remember when I was last carrying a film. To have a man's story entrusted to me has been very rare. It's in your hands. You have three wonderful co-stars, but basically George is yours for the day, he said.

Ford based the movie on Christopher Isherwood's 1964 novel of the same name and said he chose Firth for his ability to telegraph what he's thinking through his eyes, almost without moving his face, and certainly without saying a line.

Happily, for a movie that is long on close-ups and short on dialogue, Firth concurs. To me, the most interesting thing in cinema is the human face, he said.

TOO GOOD TO BE IGNORED

Time magazine's Richard Corliss said Firth makes the ache of lost love subtly, splendidly visible. Owen Gleiberman of Entertainment Weekly said his performance was bound to win Oscar attention, adding he's simply too good to be ignored.

Firth has never been nominated for a major Hollywood acting award in his own right. But in that singularly British self-effacing way, he prefers to hand much of the credit to Ford as both director and writer, and his fellow actors Julianne Moore, Matthew Goode and Nicholas Hoult.

With virtually no rehearsals and a brisk 21-day shoot, Firth had little time to prepare. He said Ford gave him complete freedom in a script that was all about subtext -- and a large pair of black-rimmed 1960s eyeglasses.

It was a bit more like playing jazz than sticking to a formal score. Everything seemed to come naturally, Firth said.

(Ford) was able to see what I was doing and come in and photograph it. It's really as simple as that. There were no instructions...Instead of trying to manipulate it, he gave me a chance and that gave me the most wonderful sense of freedom.

Firth became a national heartthrob in Britain after an infamous wet-shirt scene as the haughty but smoldering Mr. Darcy in the 1995 BBC adaptation of Pride and Prejudice.

In A Single Man, his naked body appears in a swirl of water during the opening sequence, yet the scene is symbolic of a man drowning in grief. And Firth said he had no hesitation about playing a gay man.

No second thoughts at all. I never consciously played gay and George's homosexuality isn't his issue. It just happens to be one more thing one could say about a very complex man, Firth said.

As for the awards buzz, Firth says he's in the middle of filming his next movie (The King's Speech with Helena Bonham Carter and Geoffrey Rush) in England, and that's quite a good place for me now, basically getting on with my day job.

Married to Italian film producer Livia Giuggioli and living for much of the time in Rome, Firth said his win in Venice in September was absolutely wonderful.

It was one of the most purely joyous moments I can recall. There was no campaign, no-one had seen the film and it was just a wonderful surprise. It was as good as it gets.