George Clooney is a generous man, especially when it comes to his friends. When Brad Pitt built a string of eco-homes in devastated New Orleans, Clooney purchased two. When misplaced rumours claimed that Pitt’s wedding to Angelina Jolie was to take place at his Italian home, he perpetuated the myth, hiring hundreds of tables to keep the paparazzi guessing and to ensure that they were, at least temporarily, far away from his chums.

He’s especially doting when it comes to his most recent co-star, Renée Zellweger. “With our new movie, Leatherheads,” he drools, “I realised that I didn’t even have to brief Renée, she just gets it. She can act in a film and not feel contemporary – most actors feel as though they’re from 2008 and stick out like a sore thumb. But Renée’s timeless. She’s like Jean Arthur. She’s a perfect romantic lead.”

Leatherheads, which Clooney directs and stars in, is a film cut from the same cloth as the screwball comedies of the Thirties and Forties. Clooney plays a football coach of a 1920s American football team, Zellweger the cub reporter sniffing for dirt around his new signing, Carter Rutherford (John Krasinski, from the American version of The Office). Naturally, a love triangle takes root amid the bruising touchdowns. “Leatherheads” is a moniker applied to professional American Football players in the Twenties.

Zellweger is perfectly suited to her character’s wry witticisms, divine cloche hats and ruby-red lips. The film plays like one of the classic battle-of-the-sexes films crafted with such precision and humour by the likes of Billy Wilder, George Stevens and Howard Hawks: Clooney and Zellweger swap rata-tat dialogue, while stoking the flames of their fiery relationship.

Zellweger has often been compared to Hollywood screen sirens of the past. In her breakthrough role, in Jerry Maguire, the director and producer eulogised over their discovery of a modern-day Shirley MacLaine – and Clooney’s recent words are more than mere hyperbole. “I did see a recent magazine article in which George said that he and I had been girlfriend-boyfriend ‘a little bit’,” Zellweger says, when we meet in Los Angeles. “But what the hell is that? ‘A little bit’? I’m not sure if I should be insulted or not!”

Settling back into the hotel chair, Zellweger emanates a sprightly self-confidence, her cherub-like face crinkling with humour or bemusement. “In fact, I think those comments were misconstrued,” she continues. “I think he was asked if he liked me and said: ‘A little bit’.” Nevertheless, Clooney implied that they had been together, I say. “Don’t you connect me with that man! I’d deny it until I die,” says Zellweger firmly but playfully. She laughs. “Actually, who the hell am I kidding? Scrap all that; do connect me with George Clooney. Connect me with him as much as possible!” Whatever the truth of her friendship with Clooney (years ago, reports linked the couple), Zellweger is widely dubbed as being unlucky in love. In 1992 she had a relationship with Sims Ellis, a musician, who committed suicide in 1995. Then there was an actor, Rory Cochrane, and then the director Josh Pate. When filming the Farrelly brothers’ slapstick Me, Myself & Irene, she had an affair with Jim Carrey, although that foundered when she moved to England to begin work on Bridget Jones’s Diary.

“I got to work one day on the set of Bridget Jones to a round of applause from the crew,” chuckles the Texan actress. “The rumour was that I’d been proposed to the night before. The report had the place, the size of the diamond, how much it cost, and what he said. But I was in bed the night before and he was out of the country! It’s amazing some of the things you read about yourself. I’d only been dating him a couple of months.

“Honestly, the whole story was amazing,” she says. “For a start I’ve only been engaged to one fella. Ever.” That fella was country singer Kenny Chesney, whom she met at a fundraiser for tsunami relief in 2005, shortly after splitting up with the White Stripes frontman Jack White. She and Chesney had a whirlwind romance, marrying in May of that year. The marriage didn’t last the year; it was annulled amid claims that Zellweger wanted to settle, while Chesney did not. She refuses to talk about him.

Zellweger, who is approaching 40, says that she has no plans to be a parent. “Motherhood has never been an ambition. I don’t think like that,” she insists. “I never have expectations like ‘when I’m 19 I’m going to do this, and by the time I’ve hit 25 I’m going to do that’. I just take things as they come, each day at a time, and if things happen, all well and good. I just want to be independent and be able to take care of myself. Anything else is just gravy.

“Anyway, this is all getting rather serious. You know, people might say I’m a strong independent woman, but that’s just because I hide my heroin addiction really well! I’m joking!” she offers. “Really, though, I’m very happy, I like my work, and I don’t want fame and fortune, and all the free stuff. And I don’t want people to clap for me, because I’m not that kind of person.”

At this year’s Oscars she looked ravishing in a Carolina Herrera dress, but in truth she cares little for fashion. Today she’s dressed in a long-sleeved black T-shirt and blue jeans – “I don’t know what label they are,” she says patting her behind– and she believes that life is too short to obsess over clothing. “Once in a while it’s fun. It’s nice to wear a great dress at the Oscars. But thinking about fashion every day would be like jail to me.”

Much has been written about her body and weight. Does she exercise much? “I run every day, unless something hurts. But I need it. It keeps me sane. I can’t run outdoors any more, I’ve got too many injuries from childhood that show up, and then I have to make it home. So I go to a treadmill. I listen to music when I run, so I can clean out my brain and all the emotional stockpiles, whatever’s preying on my mind. And I play basketball.”

Brought up in Texas, Zellweger was something of a tomboy, idolising an older brother who taught her how to strip down cars. When she was 9 her family built their own house. She helped out with the wiring, the tiling and digging the septic tank. These early lessons in self-reliance would stand her in good stead as she struggled to make it in Hollywood. They also gave her an “every-girl” appeal that no doubt boosted her performance as tough-gal Ruby in Cold Mountain, the role that won her an Oscar.

“I was raised in a household that was really frugal,” she explains. “It’s been beaten into me. I had no idea my dad was so progressive and environmental in his thinking. We always turned lights off, and we took five-minute showers, and we turned the heat down. We weren’t able to throw money around.” Now, as one of the most bankable stars in the world, Zellweger does have enough money, and could throw around plenty if she so desired. She has graduated to a rare position in Hollywood, being an Alist female star who’s popular with other women.

When preparing for the first of her two Bridget Jones films, she worked undercover at Picador, the London-based publishing house. One of her duties, strangely, was to collect cuttings about Bridget Jones and Renée Zellweger. She then piled on 20lb for the part. In perhaps her bravest move, she took on the part of Roxie Hart in the screen version of Chicago, spending almost a year training in dance. Next she’ll be seen in Case 39, in which she plays a social worker fighting to save a girl from her abusive parents.

“Honestly, I just want a body of work that I can be proud of,” she says. “And I think I’m getting there. Certainly Leatherheads is something that I’m proud of, although working for a good friend like George was a little worrying. You don’t want to be the one that ruins his movie! I didn’t let on though.”

She smiles her impish, unreadable smile: “not letting on” is what makes her such a versatile actress.

Leatherheads is out on April 11 2008

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