MALCOLM MCDOWELL leans forward in his armchair with all the poise of a consummate storyteller. He's recalling a day spent with a beloved aunt when he was performing in Torquay Rep in the mid-1960s. "We were walking around the harbour and she said" - at this point, his booming voice takes on a fey quality - "Ooh, Malcolm! You're so lucky! You're a lucky man. I know it. I can feel it.'" With the benefit of hindsight, this was an apt assessment of the future star of If and A Clockwork Orange. Such was his cocksure confidence in those early roles, you might think that luck had nothing to do with it; however, after surviving 40 years on screen, McDowell is the first to acknowledge that fortune has dealt him a decent hand.

It's also why you can make a case for 1973's O Lucky Man! as the quintessential McDowell film. A reunion with director Lindsay Anderson after playing the rebellious public schoolboy in If - they worked together again on 1982's less-successful Britannia Hospital - it was also his first film since A Clockwork Orange two years earlier. After playing the ultra-violent thug Alex in Stanley Kubrick's controversial adaptation of Anthony Burgess's novel, McDowell was at the peak of his powers: the angry young man of his day, his virile wink and self-satisfied smile seemingly the very embodiment of anarchy in the UK.

Yet this was not McDowell the man. He was no revolutionary. "I was a young actor trying to get a career going," he says now. Indeed, one has to look at O Lucky Man! to find the closest there is to McDowell's autobiography. Released this month for the first time on DVD, it is, according to McDowell, "the most personal of the films I ever did". It was he who initiated the project, basing it on his own early experiences as a coffee salesman. He even wrote the original first draft, reprising for himself (in name at least) the Mick Travis character from If A subversive three-hour odyssey across Britain, O Lucky Man! satirises everything from big business to the military and medical science. While Travis's time as a travelling coffee vendor was "very different from anything I experienced", McDowell still used his own existence as a template. "Even the ending - I kept saying to Lindsay, How the hell am I going to end this?' And he said, Well, just do what happened to you. You became a movie star - so that's the way we'll end it.'" The scene, which sees a destitute Travis walk into an audition off the street, ends with McDowell proffering an enigmatic smile after he is unceremoniously whacked over the head by Anderson, making a cameo as the director.

As smiles go, this was not the cocky smirk of Alex at the beginning of A Clockwork Orange, as he raises his glass in the Korova Milk Bar. This was, as McDowell puts it, "a Zen moment" - an unconscious understanding that life has a habit of throwing you curve balls when you least expect them. It was the last time that audiences were ever to see that look. Now 64, with his spiky hair a shock of white, McDowell's on-screen smile is more a sneer. Arguably the turning point was 1979's epic of excess Caligula, after which McDowell went from playing the oppressed to the oppressor, specialising in power-hungry tyrants in anything from television series Heroes to new horror movie Doomsday.

WHAT happened to this most avuncular of actors in the intervening years feels like something of a mystery. If you were to believe the 2006 documentary O Lucky Malcolm! - included as a bonus feature on the O Lucky Man! DVD - you'd think he had hibernated for 20 years, emerging finally as this ghostly version of his former self. Taking us through his early triumphs, up to his role as HG Wells in 1979's Time After Time, the documentary suddenly jumps two decades to the bloody British film Gangster No.1 (2000). As it happens, McDowell worked constantly in the interim, although the quality control was anything but high, with straight-to-video B-movies like Cyborg 3: The Recycler and The First 9 Weeks staining a once flawless CV.

When I ask McDowell how he survived this bleak period, he throws his head back and lets out a raucous guffaw. "Well because I'm still here," he cries. "The thing is, I'm a working actor. I'm not a movie star. I'm really not responsible for the quality. I can only be responsible for myself. I read the scripts and I go, God, that's a pile of crap!' But they're offering me so much money, it looks after my mortgage for the year. What am I going to do? Sit and wait for something special? There's only one Lindsay Anderson. There's only one Stanley Kubrick. And you only work with people like that once or twice in a lifetime - if you're lucky enough to work with any of the greats. And I've been very, very lucky."

With a 100-acre lemon and orange grove estate some 80 miles north of Los Angeles to pay for, you might call this the Michael Caine approach to acting. And who can blame him? After all, McDowell has a wife of 16 years, photographer Kelley Kuhr, as well as their two young children, Beckett and Finn, to support. But did it ever bother him that his career hit the skids? "No, no. Listen - I've been at this game for so long," he hastily replies. "I know what the story is. You'd better not let the highs get too high or the lows get too low. You'd better just find a nice place in the middle and get back out on the golf course."

Not that this entirely tells the full story. McDowell did let the highs get too high. After divorcing his first wife, actress Margot Bennett, in 1980, he left England for good to move to Los Angeles and be with his second spouse, actress Mary Steenburgen, whom he'd met on Time After Time. Yet shortly afterwards, while starring in Paul Schrader's misjudged horror remake Cat People, he found himself embroiled in the notorious LA party scene and heavily addicted to cocaine. "I had come to drugs quite late really - my early 30s - and suddenly I found myself unable to do anything," he says. "I think I believed what people said, that it's non-addictive, when of course it is highly addictive."

After swiftly entering a rehab clinic, he emerged intact - though it was around then that his film roles began to nose-dive. Yet, of late, McDowell has managed to defy venerable critic David Thomson's assessment that his is a "strange, thwarted career". While he is not immune to the odd howler, such as Rob Zombie's recent Halloween remake, roles in what he calls "hot and youth-orientated" US TV shows Entourage and Heroes have seen him reborn. He has also taken some of his biggest risks to date, such as playing a paedophile and child-killer in 2004 movie Evilenko. And he brilliantly paid tribute to Lindsay Anderson with his one-man stage show Never Apologise, which he premiered live at the Traverse Theatre as part of the 2004 Edinburgh International Film Festival (and later recorded for film).

Directed by Neil Marshall, new movie Doomsday also has a strong Scottish connection. An apocalyptic thriller inspired by the likes of Escape From New York, The Warriors and Mad Max, the premise sees Scotland sealed off by a giant wall after a killer virus spreads across the country. McDowell plays Kane, the de facto leader of a group of survivors holed up in a castle, wearing armour and living as if in mediaeval times. He says he sees Kane as "a King Lear kind of character", lending this action movie a sense of undeserved profundity. Though much of the film was shot in Cape Town, McDowell's scenes were all filmed at Blackness Castle on the Firth of Forth. "I love Scotland," he smiles. "To be near all those great golf courses "

As well as allowing him to work on his handicap, Doomsday reunited him with old chum Bob Hoskins, who co-stars in the film as the official who sends Rhona Mitra's kick-ass heroine into the hot-zone to try and find a cure for the virus. "I haven't seen Bob in 30 years," he muses, noting that they briefly appeared together in Royal Flash, in which McDowell played the swashbuckling lead, in 1975. "He was extremely good as a cop who raids a bordello." Even before that, McDowell recalls watching Hoskins play in an improvised show upstairs at the Royal Court Theatre in London. "I said to Bob, Do you remember?' He went, Oh, yeah! We used to say, Oh God! He's in again!''"

At the time, McDowell - who was actually born Malcolm John Taylor in Leeds and, after leaving school, spent time in Liverpool working in his father's pub - had come down to London to seek his fortune as an actor. Earning money as a messenger boy for a firm of solicitors, he spent two years playing extras with the Royal Shakespeare Company, but realised theatre was not his thing. "I wanted to try and get into film if I possibly could. I just felt an affinity with it, even then, before I'd even been in one." He struggled for a while. "I wasn't getting these jobs - I kept thinking, I could play that', but I hadn't figured out how to audition." When he did, appearing briefly in Ken Loach's 1967 film Poor Cow, he wound up on the cutting room floor.

Within a year, however, his luck changed. The moment he was cast by Anderson in If is "still the most earth-shattering in my life", he says. "It made everything possible." With the film winning the Grand Prix in Cannes in 1969, almost overnight McDowell became both a star and a pin-up boy for armchair revolutionaries everywhere. The fact that this month is also the 40th anniversary of the student riots in Paris is not lost on McDowell. He and Anderson were shooting the final scene of If - in which Mick Travis fires a machine gun from the rooftop of the school on to the parents and teachers below - at the time the riots were going on. "Lindsay held up a copy of The Times with a picture of a student on the top of the Sorbonne with a machine gun in his hand. And he went, Well, there you are. They can't say we're not topical. This is like a still from the film.' And we just looked it at agog!" In truth, though, McDowell knows that it's his role as the ultra-violent gang leader Alex in A Clockwork Orange that sustained his cult appeal over the years. "I can't tell you how many people write to me about it, or invite me to go talk about it," he explains. He recalls the first time he ever saw people dressed like Alex - now a common occurrence on Halloween, he says. "I was driving around, under the Hammersmith flyover, and I passed the tube station and out came four boys in the white boiler suits with the bowlers and cod-pieces, and I'm driving past and I put the window down and looked out, but of course they were oblivious. I was hooting with laughter."

His enthusiasm for the business remains untainted even now, not least because he seems busier than ever. He's filming Barry Munday, a Juno-esque comedy about pregnancy "from the male perspective", co-starring Cybill Shepherd and Chloë Sevigny. Then he returns to reprise his Heroes character, the ruthless kingpin Mr Linderman (never mind that he actually died in the first series; such is the enduring power of McDowell, "they got so many emails, they brought me back"). Finally, he's reuniting with Mike Hodges (I'll Sleep When I'm Dead) for a version of Thomas Mann's Mario And The Magician, based on a long-gestating script written by late Hollywood veteran Abraham Polonsky.

It seems that his only worry is that his two older children, from his marriage to Steenburgen (which ended in 1990), are planning to follow in his footsteps. While Charlie, 24, is an aspiring film-maker, Lily, 27, wants to be an actress. "I think that's extremely difficult," he sighs. "She'll just have to take her chances like everyone else. She knows it's tough. When she told me, I said, Oh my God! What do you want to do that for?' And she said, Well, it's your fault, Dad - you and Mum!' So I couldn't really complain." Still, if she is anywhere near as lucky as her father, she'll have no problem at all.