Forget Phil and Grant Mitchell and their perennial grief with the Old Bill and the trouble and strife. The most authentic East-Ender on television is Ray Winstone, a genuine West Ham fan whose very being rings with the sound of Bow bells.

He is perfectly cast as Woody in Tony Grounds' Our Boy, a moving BBC1 drama about the traumatic impact on a close-knit East End family of the sudden death of a child.

Woody is a likely lad, always ducking and diving, well-known to the police. He does a bit of building work on the side and likes nothing better than leading the boys down the pub in a rousing chorus of the West Ham anthem, "I'm Forever Blowing Bubbles".

Like Eric Bristow, Winstone knows that he will forever be cast as a crafty Cockney. "I haven't got the sort of face where I could ever be a heart- throb," concedes the self-described "Plaistow boy" with a smile, "and I've never thought I'd like to play Hamlet. Shakespeare didn't write for chappies like me. I get cast as a thug and I enjoy playing them. I understand that's the way it works. But it's not a question of being typecast because there are a million ways to play it. I'm not always just the bloke with the gun in his hand."

True enough. In recent films - such as Gary Oldman's shattering Nil By Mouth, Antonia Bird's well-crafted Face, and now this - Winstone has displayed a visceral power way beyond any simple a-little-bit-tasty, chirpy Cockney stereotypes. In the process, it has made him the hottest thing this side of a plate of chicken phal.

As he charts the emotional decline of Woody from a laddish dad to a gibbering wreck, Winstone shows himself capable of touching deep psychological chords. In an achingly sad, wordless sequence at the boy's funeral, Woody, deaf to the vicar's request to sit down, walks up and simply rests his hand on the coffin. He takes to sleeping in his dead son's bed and visiting his old playground and football pitch before pointing an accusatory finger at his wife (played by Pauline Quirke): "It's getting better for you."

As he spirals into a complete breakdown, Woody starts wandering down the middle of the road shouting at passing cars. At Christmas, he camps out in the garage where the boy's body was discovered: "I just felt that if anyone had said `Happy Christmas'," he explains, "I'd have sicked me soul up." Tough stuff.

Winstone sits on a sofa in his agent's office in front of a huge poster from Face. He is dressed as though he forgot to hand back his costume at the end of Quadrophenia; it is a Mod symphony in chocolate - from his zip-up cardy to his suede shoes.

Puffing on a cigarette, he says he was drawn to Our Boy because "it was so good to do a story about the East End which isn't just about people running around robbing banks. The characters in this are working people; they're not crying about being on the dole. They look after their kids and their mothers. It ain't about hardships, it's about a bombshell hitting a family and destroying the thing they love."

A parent himself, Winstone admits that making Our Boy did affect him profoundly. For all that, he tries not to be too earnest about his work. "On the most harrowing films, you have the biggest laughs," he reckons. "You have to keep sane. People take this job so seriously. Like the Method actors who live on a pig-farm for nine months as background research - why? As Laurence Olivier said to Dustin Hoffman when he kept running around the block to get into character for Marathon Man: `Try acting'.

"The whole thing makes me laugh," Winstone continues. "I sometimes watch myself and get the giggles. I think, `What a ridiculous way to earn a living. Dressing up and pretending you're someone else. Get a proper job, son'."

Now 40, Winstone was first turned on to acting by his father, a cab driver. "He'd pick me up from school every Wednesday and take me to the pictures," the actor remembers. "I was brought up watching films like Zulu, Lawrence of Arabia and The Vikings. At the end of 633 Squadron, he said, `Do you want to watch that again?' and we did."

Having been kicked out of drama school - "I put tacks in the wheels of the headmistress's car" - Winstone made his film debut with Scum in 1979. The director, Alan Clarke, gave him the part of the hard-nut leader of a Borstal gang on the strength of the way he swaggered down the corridor to the audition.

After Quadrophenia, The Who's scooter epic, a lean period followed for Winstone. "I was bored and doing crap to pay the rent," he sighs. "You go in and out of fashion, and I'd had enough. I thought of giving up and spent some time working in the fruit game."

Reinvigorated by appearing in a play written by Kathy Burke, his co-star in Nil By Mouth, Winstone has now made 11 films in the last 12 months. He is, as they say down Plaistow way, having it large in the film world.

The movie that catapulted him from talented character-actor to big-league lead was, of course, Nil By Mouth, Oldman's searing, semi-autobiographical account of a family ravaged by an abusive, drunken father. "The critics sat there and just went `wow'," Winstone recalls with obvious pleasure. "The film jumps out of the screen and kicks you between the legs."

He does not share some people's concern that Nil By Mouth is too unremittingly bleak to stomach. "I hope people watch it and say, `We can cross the line'," he contends. "The minute you start to compromise, you've lost it. You go for the truth of the character and don't worry about who you're going to upset. That's the thing about censorship. If you're making a film like that, holding back would be like cutting the bottom off a Picasso painting."

Now in a position to pick and choose his roles, Winstone aims to maintain quality control. "I don't like films that are patronising," he asserts. "Film-makers often underestimate the audience's intelligence. They get a format that's successful and are frightened to change it. People need their brains to be stimulated. The times I've sat there and thought, `I know what the next line's going to be' - that's frustrating."

The hardest-working man in showbiz has just completed two films, Dangerous Obsession and Sea Change, and is about to start work on another, Tim Roth's directorial debut, War Zone. The one thing Winstone hasn't yet done that he might fancy is a Merchant Ivory "white linen suit" drama. "When posh people do films, they're good," he declares, before adding with a laugh: "I could see myself on an elephant."

Now that, I would love to see.

`Our Boy' is on tomorrow night at 9pm on BBC1