If Bob Hoskins is as unambitious as he says he is, then why is he one of the hardest-working actors in Britain? And how has this squat bulldog with a Cockney accent as thick as his waist managed to become one of Hollywood's most sought-after talents?

"Ambition?" he says, pushing away a plate of prawn shells and turning up the CD player. "Listen to this. This guy's playing the Jew's harp in perfect pitch.” He closes his eyes and bliss washes over his truck-driver's face as he conducts a few delicate bars. "Sorry, you were going to ask me a question. What was it? Oh, my ambition. I really haven't got any. I just like doing it. I love the people. A lot of it has to do with me being very good to have on a set. It's a lot of laughs."

He proves his good humour on the set of Mermaids, a film shot around Boston in the US. Hoskins plays a small-town shoe-shop owner who falls for a drifter, played by Cher, and her two daughters. Much of the time he is a sympathetic backdrop for the three women's dramas, often with little to do other than place his hand on a shoulder or twist a glass of whisky. But every glance and touch has vulnerability that is so much more surprising coming from a loutish-looking guy in a leather vest and a beanie.

"The only way I learnt to act was by watching women, not just actresses but women, my own mum," Hoskins says. "Women have had to keep their mouths shut for thousands of years and a woman, without talking to you, can express herself very clearly. A man has got this sort of shield. Drama is about very, very private moments and you're not going to do anything with a shield. The only way you're going to do it is by having a physical language where you can express yourself.

"We have these incredible heroes like Rambo but we forget the heroism in ordinary people, which is extraordinary. A woman on her own bringing up her kids today, that's heroic. Not these fantasy figures where you think, how the f... can I compete with that? You can't."

The film set is a shabby sixties living room built from plywood. Between scenes Hoskins wraps his short arm around his young co-star, Winona Ryder, and starts to dance. He's as easy as old Uncle Bob. "Tiddly-om-pom-pom, tiddly-om-pom-pom," he sings. "Is that an English thing?" asks Ryder. "It's Winnie-The-Pooh," he says. "Now that's who I should play - Winnie-the-Pooh."

Hoskins is indeed built like a teddy bear, but so far his roles haven't included anyone as benign as Pooh. Among his most memorable characters have been a ruthless mobster in The Long Good Friday, a lovelorn, violent song salesman in the BBC's Pennies From Heaven, a failed gangster obsessed with a prostitute in Mona Lisa, and a private detective called in to solve a cartoonland murder in Disney's 1988 hit, Who Framed Roger Rabbit. He has also played Napoleon and Mussolini.

Looking back, it's difficult to imagine another actor in any of those films. Hoskins is absolutely real in his portrayal of working-class toughness tempered by an unexpected gentleness. Despite his long criminal record on screen, we remember him not as a baddy but as a softy. Of the roles he hasn't played yet, he says: "I'd like to make a cowboy film, a sort of swashbuckler" He swings an invisible sword. "I'd love to play the monster in a horror film - a really soppy horror film. I don't want any blood and gore everywhere."

Off the set, Hoskins remains jovial. Our interview begins in his trailer with hot toddies all round to ward off the flu that has been knocking down crew members. He is comfortable with all kinds of people, even journalists, and most particularly with himself

"I'm a short, fat, middle-aged man with a bald head and a broken nose," he says, going about as deep into self-analysis as he ever does. "I can't see that really as being Tom Cruise, can you? It's not every young girl's dream, is it? But I don't really know what I look like. I only see myself when I shave. It's very easy to convince me that I don't look a bit like I look. When I did Pennies from Heaven, the choreographer convinced me that I looked like Fred Astaire - tall, slim and lithe. When I saw it I couldn't believe it. It looked like a little hippopotamus leaping about. I thought, 'Christ, is this graceful?’”

There's no pain in the revelation but he laughs at the idea that many women find him sexy and that the American film critic Pauline Kael quoted a friend in one of her reviews, describing him as "a testicle with legs". He seems to identify more with his role in Mermaids, for which Cher cast him (released next month). Lou Lanskey is different from all his earlier characters, he jokes, because he has never killed anyone. "Lou's a very strong family man whose kids have grown up. His wife's left - she walked out without turning off the vacuum cleaner - and then this lot comes to town, Mrs Flax [Cher] and her two little daughters. For Lou it's like God has tapped him on the shoulder and said, 'It's your turn, son'. This is the best thing that's ever happened to him."

For Hoskins, too, his family is the centre of his world. On location for more than three months with Mermaids, he is aching to see his wife, Linda, a former sociology teacher, and their two children, Rosa, 6, and Jack, 4. Their photographs are scattered on the coffee table. He also has two children - Alex, 21, and Sarah, 17 - from a previous marriage. He never works during school holidays and his favourite place is his own kitchen in London's Islington.

"I made such a stuff-up of my first marriage," he shouts, mainly at himself. "I had a nervous breakdown and went through a terrible time. We had ten years of it and even my son said, 'Why don't you go? Get out, this ain't working.' Acting is like ripping lumps off yourself and if you're gonna do that all day there's got to be someone there to heal you at night, someone to hug, someone who's for ya. Without my wife I'm lost.

"I've ceased to worry about what people think of me. I'm more worried about what I think of them. It sounds arrogant but that's basically the way I am. It comes from age, security, having somewhere I can go where I'm king."

Young Bob Hoskins wasn't so domesticated. Born in Suffolk, the only child of a bookkeeper and a school cook, he left school at 15 and spent 10 years wandering. He worked as a truck driver, a window cleaner, a steeplejack, a porter at Covent Garden, a circus fire-eater. He painted, sculpted and wrote poetry. He joined the Norwegian merchant navy at 17 but left after two weeks, when his ship docked in Amsterdam and he met a hospitable stripper. He even, at his father's encouragement, began to study accountancy, but realised it was turning him into the kind of person he didn't like. So he wound up looking after camels for the Bedouins in Syria and later packing fruit on a kibbutz in Israel.

By the time he fell into acting, at 25, he had enough material to draw on for a creative lifetime. Drinking with a friend at the bar of the Unity Theatre in London, Hoskins heard there were auditions upstairs. It was worth a try, so he went up, took the script and read it as the director told him to. He was hired for the play, Featherpluckers, and spent the next three years in repertory theatre. Eventually he was in a play called Veterans, with more lines than his co-actor, John Gielgud. But, the audience wasn't laughing in the right places.

"Take a step back and count to two before you say that line," Gielgud advised him. The next night the laughs came. Hoskins hasn't forgotten that lesson in timing. "Acting is like chess," he says. "You only get better by playing with people better than you." He still likes the immediacy of theatre, but since doing Guys And Dolls at London's National Theatre a few years ago, his time has been fully taken up with film and television (including the Australian television series, The Dunera Boys).

He has never, he says, touching the wooden table, been out of work. Although he had parts in The Cotton Club and Alan Aida's Sweet Liberty, Who Framed Roger Rabbit was Hoskins' vehicle into Hollywood. He was lucky to be part of a film whose extraordinary technical advances fascinated millions of children and adults. But, at the same time, there couldn't have been an earthier Eddie Valiant. As one of the few flesh-and-blood characters in the $US40 million Disney-Spielberg animated film, he dealt convincingly with the sexy celluloid Jessica Rabbit and the evil Judge Doom. Hoskins doesn't feel transformed, though.

"Mermaids is the second job I've done since Roger Rabbit. They're both small, quiet films; they're not big noises. I've been asked to do quite a few big noises but it's not my kind of scene. Getting famous is one thing but being paid astronomical sums of money is another. I can't say I'm big box office." He makes three jabs at the air to show that his earnings are comfortably mid-way between hunger and mega-millions- a fortune compared with his finances of a few years ago. “After my divorce I was plunged into incredible debt and the bank took over all my debts, paid them off, took all my fees and paid me 50 pounds a week," he recalls.

His accountancy training, apparently, was useless. "The bank said, 'Listen son, you're going to end up in bankruptcy court and we don't want that to happen.' When I first met Linda, we were living in one room and she was feeding us. So she wasn't impressed by the big film star."

His other release last year was called Heart Condition. The film raised the awful fear that Hollywood might be the ruin of Hoskins, though it doesn't seem to have occurred to him yet. In an action-comedy that made one nostalgic for the delicacy of Mona Lisa, he played a piggish, racist detective who gets a transplanted heart from a murdered black lawyer (Denzel Washington) and is predictably reformed. For one unsubtle scene among many, he had to eat 38 hamburgers.

Maybe he looks as though he eats like that all the time, but in fact Hoskins' natural interest in food and drink is modified by the demands of his work. "Fitness isn't a question of looking good," he says. "It's a question of being alert. Say you've got to have a nervous breakdown this morning and before lunch tomorrow you have to take Tobruk 15 times - you've got to have stamina."

His actor friend and trainer, Alan Talbot, sometimes travels with him to urge him into the gym after the day's shooting. He is also accompanied everywhere by Sammy Pasha, a former London taxi driver who was hired on The Long Good Friday as Hoskins' chauffeur, stand-in and minder. "The first day we didn't know what was what so I looked after Bob and he looked after me," says Pasha, another jolly Cockney.

They've been a team ever since and often talk about "our films". "Bob's a pro," he says. "He's on time. He's not just an actor. He's been a director so he knows what's going on. We know photography, we know the lenses. We know everything that's going on."

Hoskins and Pasha recently finished another film. Co-starring with Tom Berenger, Hoskins plays, yes, another detective, this time one who runs a pet shop in San Francisco ("He thinks animals are much better than people"). At last, however, Hoskins is breaking out of his stereotype. He will appear in the title role of an Anglo-American television production of Uncle Vanya, and as a photographer of religious subjects in a comedy film called The Watch, The Favour And The Very Big Fish.

He is also preparing to direct a film of Joseph Conrad's novel The Secret Agent. If it happens, The Secret Agent will be his second directing effort. Three years ago he shot a film in Czechoslovakia called The Raggedy Rawney, about a deserter from the Hundred Years War who lived in a gypsy camp for 20 years disguised as a mad woman.

Hoskins' priorities in life are clear: the people he lives with, works with and meets around the world are what makes the rest worthwhile. He recently made a documentary to publicise education for children disabled by cerebral palsy and polio, and drove a supply truck across Europe for the exiled people of Western Sahara.

He is passionate about his friends. "My biggest fear, I suppose my biggest weakness, is terror of losing people, and I've lost a few," he says - and for a minute the man who attracts descriptions like "meatball" and "a fire hydrant with eyebrows" is stopped by tears.

"The last couple of years AIDS and drugs have devastated my friends. I keep going to funerals and thinking, f..., hang on, we could have talked about this." Although he was brought up "a total atheist,” Hoskins says that more often these days he thinks, "Well, hang on, maybe there's something else." He saw a ghost when he was 16 and working in Covent Garden. It was a cluster of lights in the perfect shape of a woman.

"One of the guys running the warehouse said, 'You've seen one of the nuns.' He said, 'You're going to be lucky. You're going to have a lucky life.'

"Well," says Hoskins, laughing again, "I'm not knocking that."