AT THIS precise moment, Hollywood star Tom Hanks wishes he was back on his desert island in the South Pacific. He has emerged from a photocall with dozens of photographers at London's Dorchester Hotel for yet another interview on a seemingly endless promotional round at home and abroad for his latest blockbuster movie Cast Away.

He glances at his watch to check the time of day before uttering a welcoming "good afternoon". As he spent several gruelling months on the tropical Fijian island of Monu-riki playing someone marooned for four years on an uninhabited island, you might be forgiven for thinking that the prospect of being castaway for real wouldn't appeal.

"It does after days like these," jokes Hanks, reflecting that a few moments of solitude instead of having to talk about "every single aspect of myself and my career" isn't such a bad idea at this particular time.

"There is great romance to be found being marooned," he says. "Everybody would like to get away to ponder the universe, starlit skies and palm trees for a while. Everybody thinks that would be great. The reality is quite formidable and to be avoided at all costs."

He knows only too well from experience the risks of desert island life - he almost died from blood poisoning after a sore on his knee became infected during filming.

"We left Fiji on a Friday and by Sunday my lower leg had swelled up to twice its normal size and I had to go to the doctor. I thought maybe he'd clean it out and give me some antibiotics to take. But the next thing I know I had five doctors running around in a panic trying to figure out what was inside my leg.

"I underwent surgery that night and was out of action for three weeks. We had to shut down the movie. I was quite close to blood poisoning. It was surprisingly, incredibly serious. I would never have anticipated something that happened to me casually while shooting could become something of a major health crisis."

Out of curiosity the actor did ask the doctor what he could have done if, like the character he was playing on film, he'd been alone on the island. "He described a process of getting the infection out of my blood that was like squeezing toothpaste out of a tube. I couldn't have done it. I would have been dead in five weeks."

There are few other actors that audiences would be willing to watch alone on screen for half of a two hour-plus picture. Double Oscar-winner Hanks is one of them, a man dubbed a latterday James Stewart for his ability to project a common man appeal that makes him likeable and believable in most roles that he plays, whether it's the simpleton hero of Forrest Gump or a gay lawyer in Philadelphia.

In real life he seems as friendly and approachable as he does on screen. If he has an ego - and given the level of his success no one would blame him for throwing a few tantrums - he keeps it out of the public view.

He not only drew on his emotional acting bank for Cast Away but went through a remarkable physical transformation. Before shooting began, he piled on the pounds. Then the picture was shot over 18 months with a break in the middle for Hanks to lose weight and grow his hair and beard to give him an authentic, emaciated castaway look.

The hardest part of losing weight was having to do it over a short period. "I wish I could have taken a pill or just eaten bacon and grapefruit for three weeks," he says. "It was the idea of four months of constant vigilance as well as two hours a day in the gymnasium doing a monotonous workout on one of three machines.

"Just how long it takes to lose weight wears you down after a while. When you're in your fifth week of a workout and counting your calories, you have to power yourself through almost by some kind of meditational trickery."

And how did his wife, actress Rita Wilson, like the difference between big Tom and little Tom? "She had nothing nice to say about big Tom and, if she put a bag over my head, she had no problems with little Tom. That goat boy look doesn't exactly conjure up sexual fantasies," he says laughing.

Emotionally, the role took its toll too. He doesn't see himself enjoying a solitary life, pointing out there's a real difference between solitude and abject loneliness. "I can understand the concept of being a monk for a while. You take a vow of silence, don't see anything, read anything, hear anything. With my personality that goes for about 69 hours and then I would probably go absolutely nuts. I have too many chromosomes of an actor. I need some sort of stimulus," he explains.

There was no one to work with during the island scenes as he's on his own apart from the washed up volleyball that becomes his companion and receiver of the one-sided conversation. At first Hanks relished the idea of doing a one-man show and couldn't wait to get down on the beach in the morning to film. That feeling eventually wore off.

"Initially it was fun. There was a degree of freedom that went along with it because I didn't have to rely on anybody, I didn't have to wait around. No one was going to screw up any lines. I could do anything I wanted. There were no rules, it was my universe," he recalls.

"But then, quite frankly, it got exhausting. I never had any time away and having to be the sole source of everything that goes on within the frame of the camera wore me down after a while. There were a couple of days, particularly at sea on the raft, I just went nuts. I couldn't wait to get off."

Inevitably, his character's time on the island alters his outlook. Hanks himself faces life-changing moments all the time, especially when for two weeks at a time "my life is nuts" - another reference to being in the spotlight whenever he has a movie in cinemas.

"You have to survive an awful lot of attention that you don't truly deserve and yet live up to responsibilities you do professionally understand. I'm always trying to balance that and what's really important.

"My kid could get a bad X-ray or I could get a call from the doctor saying I've got something growing and that would change my perspective instantaneously of what is and is not important.

"I love what I do for a living, it's the greatest job in the world. But after a while it's no longer any cause for celebration, just something else to be dealt with." At this point Hanks realises this might make him sound ungrateful for his success and adds: "Not that I'm complaining. I'm not. I'm still the luckiest man in the world."

And one of the nicest too.

l Cast Away (12) is showing now