On TV, he was a city slicker in Capital City and a hardened ex-paratrooper who turned to crime in Lynda La Plante's Civvies. Last summer, he was the British soldier being beastly to the Americans during the War of Independence in the Mel Gibson epic The Patriot. But nothing prepared Liverpool-born actor Jason Isaacs for what he had to do in the Hollywood film Sweet November - dress in drag.

He plays leading lady Charlize Theron's best - gay - friend Chaz in the San Francisco-set romantic drama and, for a night on the town, dons frock and high heels.

"The first day filled me with horror. What kind of woman was I going to going to be? I thought I was going to look like Dustin Hoffman in Tootsie," recalls Isaacs.

"Then I remembered being in New York three years ago and seeing this drag bar empty out at three in the morning. This bunch of Puerto Rican drivers, it looked to me, came out with big shoulders, hairy chests, tattoos and just sweating with laughter.

"I realised that drag for most people is about dressing up and laughing until your mascara runs. For Chaz, it's a release."

Deciding on a look for Chaz's feminine side proved a problem, especially the boobs.

"The first ones they gave me were in proportion to my shoulders and I looked like Anna Nicole Smith with huge, huge melons in front of me," he says.

"Then I put in these silicone bra fillers and looked like Kate Moss. We ended up with inbetweeny things. I have a new respect for women and the whole circus of walking on high heels. How anyone does that, I don't know."

His long, false fingernails posed a dilemma too. Not just how to make a phone call ("it took me two days to realise you have to dial with a pencil") but how to pull up his tights after going for a pee. "Thank god my girlfriend was on the set. I screamed for her, she came running across and pulled up my tights for me," he says.

She was less than impressed with his drag act. "She thought I looked repulsive. She wouldn't even put her arm round me on the set. She thought I was disgusting."

After his turn as scene-stealing Colonel Tavington in the Mel Gibson epic The Patriot, Isaacs needed a change of image, particularly as some Brits took exception to the portrayal of the military man committing atrocities. Isaacs found himself on the receiving end of personal abuse as a result of his villainous performance.

"I thought that was an extraordinary misjudgement by a lot of journalists," he says. "The notion that the British abroad have always behaved impeccably is laughable. So is the idea that we were abiding by the Geneva Convention 200 years before it was thought of. It was the same on both sides.

"A lot of papers objected that the villain was British - in a film about the American Revolution he's not going to have a KGB drug lord. I'm glad in a way about the reaction because it meant the film worked. People really hated me and that's what a good villain does. I really got under their skin. People just wanted to have a go at me."

That was one of the attractions of Sweet November, although he jokes: "It's not such a large step from British army officer to drag queen, is it?"

He reckons that Chaz is further away from his own character than Tavington because Chaz is so incredibly well-balanced in his life. "He's like we'd all like to be. He's got his love life and his work in perfect harmony," says Isaacs.

"I'm so used to killing people or being killed or ripping children apart limb from limb that it's hard to play someone who's just giving life."

He felt that Chaz was a "very well-rounded and interesting man" who avoided being the gay best friend or neighbour movie clich while providing the voice of sanity. Director Pat O'Connor eased his initial worries about the role. So did thinking back to the gay best friend with whom his girlfriend used to share a flat.

In the original script he was called Chad which, he suggested, was not a very English name. So he became Chaz, named after the character Isaacs played in two series of ITV's Capital City. "He never had a girlfriend and I thought what would happen if he moved to San Francisco. I decided he'd come out of the closet," he says.

The other attraction was that he was doing a play at London's Royal Court when the Sweet November offer came along. "It was a great part, I love Chinese food and San Francisco has three Chinatowns. I'd been in rainy London doing a very gritty, realistic play and it was time to get a frock on."

Despite his American success - he was also in Armageddon - this country is still home and he sees no need to move to the US. "I auditioned for The Patriot on tape in my front room in Hampstead. The Hollywood films I've done haven't been shot in Hollywood," he says.

* Sweet November (12) opens on July 13.