For Bob Hoskins there is no 'curse of the actor'. You just go in, enjoy yourself and bosh - job done. The problem, he tells Simon Hattenstone, is knowing when to stop acting in real life

Bob Hoskins says he's still waiting to be found out. He hasn't got a clue what he's doing in this business. "I feel I'm the wrong name on the right list," he says. "Keep going, keep prodding, and nobody'll notice. When I told my relations I'm gonna be an actor, they said: 'Don't be fucking daft. Forget it! You've got to be kidding, aintcha?'"

He's got a point. A bullfrog of a man with a boxer's nose and a right gob on him, he's hardly your conventional lead. But he's been working for 40 years now, and in that time has created some of the most memorable characters in television and film - Arthur Parker, the frustrated songsheet salesman in Pennies from Heaven, Harold Shand, the psychotic gangster in The Long Good Friday, lovelorn George in Mona Lisa, the eye-popping private eye Eddie Valiant in Who Framed Roger Rabbit. He does hard bastard and soft bastard equally well. In his new film, Sparkle, he is playing one of his touching - and touched - softies.

Not surprisingly, acting wasn't his first job - it came along by accident one evening in London in the late 1960s. Hoskins turned up with his mate for an audition at the old trade union theatre, the Unity. He was just there for a drink, it was his friend who wanted the part. Right, next, said the casting director, pointing to Hoskins. Before he knew it, he found himself on the stage reading from the script of a play about a young thug. He got the lead, and that was that. He didn't have any training or theory behind him, but he was good at pretending to be other people. "There's two things I love about this business. One's acting and the other one's getting paid for it. The rest of it is a mystery to me. But I ain't got the faintest idea what the fuck is goin' on, you know. I've read Stanislavsky, and I thought, well, this is obvious."

Ignorant sod that I am, I ask if he means the Method, as thesps like to call it. "Nah! Nah, that's Lee Strasberg, that's bollocks! Like how to look busy. It's just looking busy, impressing the boss. That's bollocks, going through all this cobblers. Living it out and all that. Bollocks. Total cobblers!"

I think I know what you mean, I tell him - for example, with The Long Good Friday it's pointless killing a few people just to get into character. "Exactly!" he says. "I'm out the door in a flash. Gone. Let's face it, some of the characters I've played you can't take home to the wife and kids."

Hoskins grew up in Finsbury Park in north London, his father a lorry driver, his mother a nurse. He left school at 15. Was he as hard as he seems? "Naaaah. You don't end up with a face like this if you're hard, do ya? This comes from having too much mouth and nothing to back it up with. The nose has been broken so many times." Was he mouthy? "Oh yeah, plenty of courage. I'm the soppy sod who got up again."

Hoskins in Who Framed Roger Rabbit. Photograph: Moviestore Collection/REX

It was in the late 1970s and early 80s that he produced his most outstanding work, partly because he was more fussy with his choices, and partly because Britain was rich in writers and directors. On television, Dennis Potter mingled genres and explored the subconscious in ways that hadn't been seen before. Was he aware that Pennies from Heaven was special when he was making it? "Nah. The thing was at the time the BBC were quite frightened of it. Whasisname, Piers Haggard, the director, asked me to take me clothes off - I come home, take me clothes off, put me pyjamas on and go to bed, about as sexy as a bag of Brussels sprouts. But he says, 'I want full frontal.' Well, Bill Cotton [then controller of BBC1] went fuckin' bananas. 'We can't have that,' he says, 'If you show Hoskins' cock on the television we will get letters of complaint.' Dennis, without a beat, says, 'No Bill, you'll get letters of sympathy.' Hahahahaha!" Hoskins roars.

What happened to the golden age of TV drama? "Gawd knows. It's all fucking live television, isn't it? It's all bollocks. Living television is the cheapest way to make TV and the cheaper they make it, the more money for the executives."

Hoskins is now 64, but has no plans to retire. The thing is, he says, an actor can be in an iron lung and you can still give him a part. And now, with his age and status, he's enjoying himself more than ever. "You reach a point where the cameo is the governor. You go in there for a couple of weeks, you're paid a lot of money, everybody treats you like the crown jewels, you're in and out, and if the film's a load of shit, nobody blames you, y'knowwhadimean. It's wonderful."

Maybe for you Bob, I say, but not always so wonderful for us. The cameos can frustrate the viewer, and unbalance a film. In Sparkle, for example, you wish he was in the film longer. He laughs off the criticism. "Always leave 'em wanting more, son!"

Hoskins has always liked his money. He is probably better known these days for the irritating British Telecom campaign than for his movies. For years, people stopped him in the street and told him: "It's good to talk." He was paid a huge amount by BT, but was it worth it? "You're joking, intcha? I couldn't believe it. It was un-be-lie-va-ble." So little work, so much money. Of course, he'd do it again if he was asked. "The worst thing that happened to me was Madonna getting stalked by a fella called Bob Hoskins, and I had fuckin' hundreds of people come up to me, and say 'It's good to stalk.' Bastards! Hahaha!"

He accepts there have been flops, and films he's detested, but that's the nature of the game. "The worst thing I ever did? Super Mario Brothers. It was a fuckin' nightmare. The whole experience was a nightmare. It had a husband-and-wife team directing, whose arrogance had been mistaken for talent. After so many weeks their own agent told them to get off the set! Fuckin' nightmare. Fuckin' idiots."

Hoskins insists that acting is about having a good time, getting paid, getting home and getting the role out of his head. Bosh. The one time he found this difficult was playing Hilditch, the sex abuser, in Atom Egoyan's Felicia's Journey. "I'd finished and two weeks later Linda [his wife] said to me, 'Bob, you do realise you are behaving very strangely at the moment.' I went fuccccccck! Had a triple flush." Was he aware of it? "No." Had he gone quiet? "Very quiet."

Hoskins in The Long Good Friday. Photograph: Everett Collection/Rex

Dig a little deeper, and you begin to realise that his attitude to acting is not quite so glib after all. His father recently died, and this was when he truly realised that acting is anything but a nine-to-five job - that it is more deeply rooted in his psyche than he'd like to admit. For the first time all afternoon, he talks quietly - about his love for his dad, how he drove him round Regent's Park when he was dying because that's all his dad wanted to do. "He didn't want to look at the roses or have a cup of tea or anything, he just wanted to be driven around. The police stopped us a few times and said what are you doing, and I said I'm driving him around ..."

When his dad finally died, he was bereft, but left with a horrible numbness. "People talk of the curse of the actor ..." He stops and starts again. "Acting is like therapy, expressing the most extreme emotions and passions that a human being's capable of. Then inevitably tragedy hits your own life, and all your family and friends gather round quite sincerely and openly show their pain, share their grief and comfort each other.

"But you immediately click into acting mode, and you know that you're fucking acting." He sounds distraught as he tries to explain the emotional vacuum. "You just can't help going into it, and it's dishonest. It is really fucking dishonest. You're starting to act, not expressing yourself properly. So you close down, and then you wind up on the outside. So fucking lonely. People cry, and you start doing that and you know it's a technique, this is bullshit. It really struck home."

Has he been able to get beyond this yet? "No, not yet. The point is you're stuck with it. I've still got it. It's still there. It's like a big fucking knot in there. I've got no way of expressing it."

Big bollocksy Bob Hoskins now seems so small and vulnerable - and all the more likeble for it. He once said acting had saved his life. I ask him what he meant. "Well, it's given me everything I've ever wanted. It's given me a job that gives me a buzz, it's paid me a fortune, I live the life of a rich man, it's given me a chance to educate my kids, given them the education I never had." What does he think would have happened to him if he'd not become an actor? "Probably rob banks or something." He pauses. "I'd probably be dead."

· Sparkle is released on August 17