For a man described as "the icon of macho movie stars" and "a living legend", Clint Eastwood looks remarkably ordinary in the flesh. You expect someone bigger and more imposing, not a figure that could be any other elderly American tourist staying in a London hotel.

The legacy of his screen image makes you expect him to pull out a gun and snarl: "Make my day, punk". Or strike a match to light a cigarillo clamped between his teeth as he did as the poncho-clad Man With No Name in the Dollars spaghetti westerns.

The reality is different. At 73, Eastwood looks fit, healthy and agreeably grizzled. The secret of what some would call eternal youth is, for him, feeling and thinking young. Having young children, as he does, keeps you young too.

"You have to take a mega choice early in the game - take reasonably good care of yourself and just enjoy life and keep learning something new every day," he says.

"I learn something new every picture, and in everyday life you learn something new and study something new. That keeps you young. If you just level off, then you just sort of vegetate."

Eastwood's appetite for work shows no sign of abating after a career spanning four decades. He's come a long way since one of his earliest screen appearances as a $100-a-week contract artist opposite a talking mule in Francis In The Navy.

The statistics of his career are impressive. He's starred in 45 films (appearing in 56), directed 24 and produced 19. He's combined producing, directing and starring 12 times; directed and starred in another nine films; and served as producer, in a variety of directing and acting combinations, no less than 13 times.

He's also careful with other people's money. Even the press notes for his latest film, Mystic River, praise him as "perhaps the most conscientious film-maker who ever got behind a camera". He's well-known for wasting neither time nor money, bringing in pictures for the kind of money other film-makers spend on catering alone.

"I've never been a luxury director who needed five times what you need. I want what I need to make the picture and nothing more," he says.

He's never been afraid to mix commercial pictures with smaller more independent ones either. After a poor spell, with pictures like Blood Work and Space Cowboys, Eastwood the director is back on form with Mystic River. He's content to stay behind the camera, directing a cast led by Sean Penn, Kevin Bacon and Tim Robbins.

This story of three childhood friends whose past comes back to haunt them in later life is already being mentioned for Oscar nominations. He prefers not to think on that level.

"I'd like to see the picture go out and have a nice life and, if that life includes anything else somebody else suggests, that's fine. The picture was made to go out and hopefully be provocative to people's minds, and that's as far as I can take it," he says.

Back in the mid-1980s, long before Schwarzenegger ever harboured political ambitions, Eastwood was using his movie muscle to win the election as mayor of Carmel, the Californian seaside town where he still lives.

Our meeting came hours after Schwarzenegger became Governor of California. Eastwood smiles the smile of a man glad not to have the worries that come with office as he says: "It's going to be interesting now he's got what he wants. Now the nightmare begins. More power to him. I wish him good luck. The state of California can certainly use it right now, and he's gonna need it. He may just be brilliant and I'm sure we're all hoping that."

Asked why so many actors want to be politicians, he turns the question around: "Well, most politicians want to be actors. It's the logical tool for a politician, especially in this electronic media age. You have to be up in front of people and a charismatic performer like Arnold is a strong presence. That's a great advantage, one that the former governor didn't have.

'Ronald Reagan was a good example. They called him the great communicator. He was a person that could make you feel very homely, very comfortable, whether you agreed or disagreed with the decision or particular political position he was taking.

"A lot of politicians now do everything by focus groups and find out what the general population wants. Then they go ahead and vote for it. Sometimes in order to be a really good politician, you have to go ahead even if it's not terribly popular. You have to make decisions that you believe in."

He adopts the same principles as an actor and film-maker. He does it his way, not letting studio executives or test audiences determine the final cut of a film. "I make the film I want, and then people like it or don't like it - and that's something they're going to have to deal with," he says.

"You should make the film you intended, the way the writer intended and your interpretation of what the writer intended, and go from there. A lot of great films, like Sunset Boulevard and Lost Horizon, have been changed around after they've been tested. By and large, I've gotta go with the hand that we've played."

His performance style too has that instinctive, unplanned feel. Richard Burton, with whom he starred in Where Eagles Dare, called Eastwood's acting style "dynamic lethargy". Eastwood himself prefers to call it understated type of acting.

"I'm not very objective about myself, to tell you the truth. I'm just hanging out and whatever I do is strictly on a spur of the moment, the instinct of the moment," he says.

"As I'm maturing, I'm more interested in directing than acting. I've always been more interested since 1970, but I stayed with both of them in order to get the films done."

Now he's content to let other actors carry the burden of performing in front of the camera. Directing Mystic River, he found himself giving orders to four leading actors - Tim Robbins, Sean Penn, Laurence Fishburne and Kevin Bacon - who've all directed in their own right.

He found that an asset as he's always felt that every actor should direct at some point in their life, and that every director should act. That way, everyone understands the process.

"You hear about actors being late and all that sort of stuff. You never find that with an actor who's directed, because they understand all the problems that a production is going through.

"These fellas have all done it and all done it very well. It was great for me. They understand the language."

l Mystic River (15) is now showing in cinemas.