Diamond geezer, smug git, or filthy-tempered old fart? Bob Hoskins presents much the same problem as Michael Caine - when he's in chirpy Cockney mode, doing his familiar anecdotes, he seems likeable enough, but you know it's an act, and you can't help noticing that there are whole chunks of his interviews you could almost recite by heart. And when something goes wrong and he's thrown off-script, he becomes monosyllabic, graceless and sour - Eleanor Mills of the Sunday Times met Hoskins on a bad day and found him 'the rudest, most disagreeable person I've interviewed'.

He is not rude or disagreeable when I meet him, but it is a bit disconcerting that he says he 'can't see the point' of doing interviews. He is supposed to be plugging the big BBC Christmas show The Lost World, in which he stars, and has been installed in a central London hotel - he lives in Hampstead - for interview purposes, along with a PR and his driver, Sammy Pasha, who goes with him everywhere. The trouble is, Hoskins doesn't seem to remember much about making The Lost World, except that they did it in New Zealand and he liked the people - 'They haven't been sort of corrupted by ambition' - and the scenery. But the truth is, he has made so many films in the past two years, in so many different locations, he can't really remember them all.

Like his friend Michael Caine, he makes far too many films, so that the good or even great performances - The Long Good Friday, Mona Lisa - are swamped by the dross. Several of his recent films seem to have disappeared without trace. There was supposedly one in the pipeline called The Sleeping Dictionary, and another called Where Eskimos Live, and another called White River (or maybe that's where eskimos live) and one I would dearly love to have seen called Live Virgin in which he played 'a pornographer with a dick tattooed on his head'. Where are they now, eh? He always says that he chooses scripts by giving them 'the cold-bum test' - taking them to the loo to read and then deciding they must be good if he reads them long enough to get a cold bum. But you'd think by now he might have noticed that the cold-bum test produces signally poor results and it might be wiser to sit fully clothed in an armchair and read a script carefully from start to finish.

He doesn't even seem to know which are his good films. When I asked what he considered his best performance, he said sulkily, 'I haven't the faintest idea. With me, I remember doing it - seeing it afterwards has got nothing to do with me. I've watched films and even forgotten I'm in them.' Anyway, he doesn't go to the cinema except when Linda, his wife, makes him: 'I spend all my fucking days making films, I don't want to waste my bleeding spare time watching them.' So this is a man out of love with his career, or who knows that his best is behind him.

He swept through the 80s with a run of good films - The Long Good Friday, 1980; The Cotton Club, 1984; Mona Lisa, 1986; The Lonely Passion of Judith Hearne, 1987. But Who Framed Roger Rabbit, 1988, was a nightmare to make, and left him exhausted, and perhaps disillusioned with Hollywood. As he says, 'Hollywood does exactly what it says it's going to do - makes you rich and famous - and I thought, "Right, I'll sign on for that, I'll have some rich and famous."' But he never really adapted to the town, in fact he never moved there, he was always a Londoner. 'There's nothing wrong with Hollywood but it is a town that is completely based on vanity, its whole function is vanity. But I haven't got anything to be vain about! I'm just a short, fat middle-aged man with a bald head.' His last major Hollywood vehicle was Super Mario Bros in 1993, which turned into an 'absolute nightmare', and he decided, 'I've got enough money now to be able to say, "Fuck 'em".'

Turning his back on Hollywood probably meant kissing goodbye to any chance of ever winning an Oscar, but he claims not to mind. He was up for Best Actor just once, in 1986 for Mona Lisa, and he remembers it as, 'The tattiest do I'd ever been to in my life, so tatty I couldn't believe it. I went downstairs to the bar and there was Jimmy Woods, Dexter Gordon, Bill Hurt [the other Best Actor nominees], all in the bar and they said, "Sit down, Bob. Here's to Paul Newman." I said, "What're you talking about? I'm going to win this." And Jim said, "Listen. Have I given an Oscar-winning performance?"' And I said, "Yes." "And has he? Has he?" [pointing to the others] and I said, "Yes." And he said, "Has Paul Newman?" And I said, "No, he hasn't." And he said, "Well, here's to Paul Newman." And by the time Newman did win it [for The Color of Money], we'd all been in the bar long enough, we were in hysterics. I've had prizes, you know, and they're all in the cupboard. Some are so ugly you don't want to look at them.'

Nor does he hanker for a knighthood, like his friend Sir Michael Caine. 'Nah, it's not for me. It's like a bowler hat, you know - they look great on some people but not on me. I'm sort of soppy. I hate being called sir, anyway. Michael's wanted a knighthood for years, he thinks it's lovely. It's actually done Michael a real favour because he's settled down. He's now been recognised for what he's done and it's right for him.'

Hoskins says he would be heartbroken if told he would never make another film; he says that being an actor is a great life. But you sense a great burning frustration in him, an anger with himself for having let his career slide. He once said that you knew you were on the skids if you started accepting roles you wouldn't even have looked at two years ago, but that must have happened to him quite often in the past decade. So why does he do it? Money? He claims not to care about money, but he mentioned two jobs he'd accepted for the dosh - Super Mario Bros and then the BT ads ('It's good to talk') because he needed to buy a bigger house when his mum died so his dad could live with them. It might be that, having grown up poor, he considers it immoral to turn down big money.

What is so frustrating is that he can be so good. Do you remember that scene towards the end of The Long Good Friday where he kills his son, and his face seems to dissolve, like a Francis Bacon, and turn into a baboon's snout? Alas, The Lost World is not in that league. He plays Professor Challenger adequately enough, but I was amazed when he told me he had had to put on a posh accent for the role - I hadn't even noticed he was trying.

On the other hand, there is a film coming up in January called Last Orders in which he is absolutely brilliant, subtle, moving, intelligent, utterly convincing, especially in his scenes with Helen Mirren. It's based on a Graham Swift novel about a bunch of old boozers and the cast is full of veteran British thesps - Michael Caine, Helen Mirren, Tom Courtenay, David Hemmings - all acting their socks off, but when Hoskins and Mirren are together they soar into a different league. I think this might explain why Hoskins's performances are so variable. He needs to act with, or against, another good actor to bring out his best. It's as if his talent is a sulky little crab that has to be coaxed out of its hole with titbits of carrion. He told an instructive story about how he agreed to do The Lonely Passion of Judith Hearne with Maggie Smith right in the middle of doing Roger Rabbit because, 'You don't say no to a chance of acting with Maggie Smith.' But he was exhausted at the time, so he thought he'd just coast through it, play support to Maggie Smith. 'But Maggie, she's not having it. She says, "I'm not a horse and you're not a carriage. Pull your own weight."' It's a pity he can't make more films with a Maggie Smith or a Helen Mirren telling him to pull his own weight.

He says he doesn't prepare for films at all, there's no point because filming is a team effort. And he can learn his lines very quickly, often while he's in make-up or walking to the set. (Interestingly, he says that being dyslexic, which he is, helps you to learn lines, because you can't skim or get the gist, you have to learn every word in its right place.) But it means that if he arrives on a film and finds it's a dud team, he's liable to be a dud player.

I would guess - I am speculating wildly here because he is so bad at explaining himself - that his basic problem is depression. He says he's not a manic depressive, he doesn't spiral off into highs, but he admits that he does have 'down' periods when he tends to go quiet and morose and doesn't want to see anyone. Linda loves 'getting the frock on' and going out to showbiz parties, but he hates them, he finds them hard work, he never knows what to talk about. Also, he says, when he's away filming, he gets very homesick very quickly and phones Linda at least once a day but often more, until eventually she will say, 'Are you sure you're all right?', and he'll say, 'Yes, fine, fine', but she knows from the tone of his voice that's he in a bad way, and will say, 'Right, I'm coming on the next flight.' But for the past two years, with their children, Rose and Jack, doing A levels and GCSEs, Linda hasn't been able to get away, and he's spent a lot of time on his own, in these godawful locations, making films that he probably knows in his heart of hearts won't be any good.

He has said that when he was younger, before he married Linda in 1982, he often used to fear madness. And in fact he did have a nervous breakdown when his first marriage ended, and went to a shrink for a few months, but the breakdown was eventually cured by Verity Bargate of the Soho Poly. He would drop in on her on his way back from the shrink and she would say, 'You're mad going to him - you're giving all your best plots away!' She said, 'If you're going to have a nervous breakdown, do it in my theatre.' So he wrote a one-man play called "The Bystander" about a man having a nervous breakdown. 'It was about a man looking through a hole in the wall. Because when you are in that state it's like living in a bubble, it's just a bubble of grief. You can be in a room full of friends but you're totally isolated.' And somehow doing the play pricked the bubble of depression and he was cured. But he is still, he says, always drawn to mad people, which is why he likes acting: 'Because everybody in this game is mad, completely barmy. And I find insanity so attractive, you know.'

It is perhaps the hint of madness that makes his acting so powerful - he can convey a sense of seething, inchoate emotion that always keeps the audience guessing as to when it might erupt. In real life, too, he is obviously swayed by strong emotions, perhaps all the stronger for being unarticulated. He is easily moved to tears - he can't talk about Chicken Shed, the theatre group for disabled children that he supports, without getting choked. And Sammy Pasha, his driver, says that he is always stopping the car to give money to beggars. He is wildly impulsive; several times he's dashed into a florist's and said, 'I'll take the whole shop' and told them to send all the flowers to Linda. Then he goes home to find her grumbling, 'What am I meant to do with all these flowers?' He always portrays her like this, as a sort of earthbound 'Er Indoors relentlessly pulling his feet to the ground. But this is obviously what he loves about her: her steadiness, her strength. He was always monogamous by nature - he says he found the 60s 'emotionally very confusing - all the one-night stands and all that, when you woke up and said, "Are you going now? Oh."'

But in all this churning emotion, does he also have a violent streak? 'Oh yes, it is there.' And does it ever break out in real life? 'No, no, I'm as calm as a Buddhist monk.' Really? His first wife, a teacher by whom he had two children before he was famous, once told the Sun he was violent. Was that true? 'Not really. We had violent rows. Really bad, terrible rows. But no.' Did he ever hit her? 'She hit me a few times.' But other people have found him frightening - look at the way he terrorised poor Eleanor Mills. Yes, he concedes, he was ' very rude' on that occasion, but filming had gone on three hours over schedule and he was supposed to be cooking a dinner party at home. He is aware that when he is angry, he is more frightening than he means to be: 'People have got an impression of me as being very violent but I've hardly ever had a fight in my life. Like, I'll lose my temper with Linda and she'll say, "Oh, shut up!" and I'll go, "Oh, all right."' But often, he admits, 'I have been extremely angry about something and I think I'm just making myself heard, and then I realise I am frightening people and I think, "Oh dear - it's just bullshit, love, take no notice." I mean, I am a very good actor!'

Partly what makes him frightening is his powerful physicality. For such a short man, he seems alarmingly huge when you're in the same room. Pauline Kael called him 'a testicle on legs' - she must have known some funny testicles, but she's right in suggesting that he exudes, not sex appeal exactly, but an extraordinary masculine charisma and confidence. You would think he might have had a complex about his shortness when he was growing up, but his mum always told him, 'Listen, if people don't like you, fuck 'em, they've got bad taste.' 'And I totally believed her! I still do!' Anyway, his looks certainly helped him when he started as an actor: 'In the theatre my shape was my total advantage. You get these very tall sort of graceful people with wonderful voices, then I'd walk on, this cube, and everyone would say, "Who's that?", and people remembered me.'

Presumably that is why his career took off so fast. He only stumbled into acting by chance (he says, though I'm not sure I believe him) in 1968, when he accompanied a friend to an audition at the Unity Theatre and was drinking in the bar when someone said, 'You're next', and pushed him onstage. He felt comfortable the minute he got there: 'I felt as if I was at home. I'd always painted and written and been quite arty, I suppose, or creative. But it's so lonely. And all of a sudden there was other people in the playground.'

Up till then he'd been a porter, nightclub bouncer, fruitpicker on a kibbutz, circus fire-eater, window cleaner - he had no particular ambition, he just wanted a good time. But then he got the part at the Unity Theatre, got an agent, and within two years was acting with John Gielgud in "Veterans."

In the beginning, he was totally committed to theatre: 'Everything was thea-taw. Telly and films were for the scallywags. But then I noticed that anybody who had made a telly or a film always got the best parts, regardless of talent! So I thought, "Oh, I'm going to get a telly, that'll guarantee me a job in theatre for life." But then once I got in front of a camera, I got interested in the lenses, and I got talking to this cameraman who became a mate, and he said, "I'll change the lenses", and I started to see what lenses can do.'

He learned about acting, he says, not from watching other actors but from studying women. 'Men are completely emotionally dishonest, whereas women have an emotional honesty which is extraordinary. And drama is about private moments, it's about the things you don't see in the street, and men don't show that. So I decided to watch women. I became a stalker, I suppose! It's got nothing to do with femininity, it's to do with emotional honesty. If you go home one night and there's champagne on the table with your dinner and she's done up but she's pissed off, you know it. You know where you are with a woman. You don't know with blokes. And that's basically how I learned to act - just watching women.'

But he also got two useful pieces of advice early in his career. One was from John Gielgud, who told him how to maximise the impact of a particular line by stepping back, counting to two and then delivering it - and it worked. 'I got a round every night! So every thing I've ever done since, there's been a line where I've stepped back two paces, counted two - and got fuck all! It was just that line, and he knew it. His timing was immaculate, absolutely extraordinary.' The other piece of advice came from Burt Lancaster, when they were making Zulu Dawn - 'a most appalling film' - in Africa. 'There was this scene where Burt came up in the middle of the night on a white horse, and I had this great speech and I thought, "I'm working with Burt Lancaster!" And I was giving it the bullshit. And he turned round to the director and said, "Give me five", and got down from the horse. "Come with me, lunatic. The aim of the game is that", and he frames a close-up with his hands. "Stick your hands in your pockets and just say the fucking lines." He said, "Watch Barbara Stanwyck - she's the master, she never moves." And she doesn't. It's incredible, she just stands there and the camera goes in and in and in - and then when you get there, it's all going on.'

Hoskins has directed a couple of films, the toe-curlingly sentimental The Raggedy Rawney, which he wrote himself, and a children's film called Rainbow. But directing, he knows, is not his metier: 'I just got fandangled into it.' He much prefers acting: 'Being an actor is the best job in the world - you're pampered, you just have to walk into make-up and everyone says, "Would you like a cup of tea?" and I love all that.' He knows the business has been good to him, that he might have ended up a window cleaner without it. But at the moment he is turning work down and giving himself a long rest. 'I really don't want to work. I'm just tired. I've done two years of back to back to back in places like Bosnia, Borneo, Poland - not the best locations - and I've had a ball but now I'm just empty and tired and I want to spend time with my family.' He'll be 60 next year. Perhaps it's time for a good long rethink of his career, and finding some better substitute for the cold-bum test.