He's seen off Grant and Nick Cotton to become Walford's longest-serving hard man. He's fought with half the Square, and slept with the rest. No wonder 22m viewers tuned in to find out who shot him. As EastEnders moves up to four episodes a week, Miranda Sawyer meets Steve McFadden to find out what a Rada-trained actor is doing with Phil Mitchell

At the end of this interview, I say to Steve McFadden, 'You're not at all how I thought you would be.' He raises his eyebrows. Explanation required. I say, 'I thought you would be more, erm, more...' Oh dear. I don't want to be rude.

'Hard work?' says McFadden. And laughs.

Well, you can hardly blame me. If you were to judge McFadden by his cover, meaning by his EastEnders' character Phil Mitchell, you'd expect an hour in his company to be a testing affair. If he wasn't wheedling your knickers off just to annoy your fiancé, he'd be trying to rob you, or hit you, or frame you for attempted murder. He'd drink you dry, nick your missus, drive your husband away and sell your assets to your sworn enemies. Or, worst of all, he'd marry you. And he'd cause you all this grief while gazing at you with an expression that says 'What? What did I do?' Phil Mitchell always looks as though he can't believe that the other EastEnders think so badly of him. He stares out from under his number one haircut like a deeply troubled potato. Walford's King Edward of pain.

And naturally I thought Steve was the same as Phil. When you meet a soap star, it's not like meeting Robert Carlyle or Jude Law or any actor who has played varying parts in their career. If you meet Jude Law, you think: there's Jude Law. If you meet June Brown, you think: there's Dot Cotton. Soap stars play the same character over and over again, two, three, four times every week. You rarely see them act another part: they don't have the time. That's why soap stars never get any critical acclaim. No one - viewer or reviewer - believes that they're acting. We think they're just being themselves. Because we never see them as anyone else.

Anyway, because of this, for the first quarter of an hour of meeting McFadden, I kept thinking, 'Why's Phil Mitchell being so nice? What scam is he trying to pull?' But then Steve started talking about going to New Order gigs in the early 90s, and Phil slipped away. Phil Mitchell would never listen to New Order. More of a meaningful US rock man, I bet. REO Speedwagon. Or Limp Biskit.

We talk in a functional, strip-lit green room just off the EastEnders set. It's 6.30pm, the end of a long day's filming for Steve. He settles into a sofa in his dark blue polo shirt and jeans, and explains that actually, in those days, he did more than just check the occasional New Order concert: he used to drive up and down the country to see them with his mate Danny, a mad fan. 'Thinking about it makes me feel romantic about the past,' he muses. 'Everything was a bit slower then. EastEnders fitted in with your life. Now, your life definitely has to fit in with this. There doesn't seem much time to stop.'

McFadden will have even less time to stop, as of next week, when EastEnders increases its weekly episodes from three to four (making the Sunday omnibus a Gone With The Wind epic). This comes on top of a purple period for the soap, with producers and writers injecting life into a once-tired format by introducing new families such as the Slaters and twisting long-established characters into previously unimagined situations. The reward: EastEnders is now the nation's most popular soap regularly trouncing Coronation Street. Everyone on the show is working flat-out trying to fill in the extra half-hour. And, as one of Walford's most prominent residents (the 'Who Shot Phil?' episode got the show's highest figures ever - over 22m viewers), Phil Mitchell has a lot to do.

Not that he hasn't been busy anyway: what with being shot, and diddling the court case, and a kidnapping coming up... it's a far cry from McFadden's 'let's drive 400 miles to a gig' years, when he first started on EastEnders in 1990. Then Phil was the quieter half of a double act with his brother Grant, and McFadden recalls getting weeks off, or days at least. Even when he was needed, he didn't have so much to say. 'I remember I'd have these scenes with Mike Reid, three-page scenes, and he'd be going on, loads of lines, and I'd just have to say "What do you mean?" Or "Leave it!" All I had to get right was my cue.'

Still, McFadden's up for all the extra work. Today he's been stoking a burgeoning re-romance with Sharon, and doing a lot of 'physical stuff' to do with the kidnapping (Dan nabs Mel, and Steve and Phil join forces to track them down). 'I'm getting into the comedy bit at the moment,' says McFadden. 'Over the years you start to see how ridiculous it all is. You know, when you're on your fourth wife, and you've lost four children... One of the prerequisites of any character in the show is to have a very short memory. Like, the week before the kidnapping, me and Steve are rowing, but by Monday evening, 8.15, me and him are the dynamic duo, like the Batman & Robin of EastEnders.

He says he learnt quickly not to let character inconsistencies worry him. A couple of years into EastEnders, Phil married a Romanian refugee, and Steve 'pulled my hair out' trying to make sense of it. 'A kind of perverse enjoyment of making the ridiculous work came over me and it's stayed ever since. It's the writers' job to throw stuff at you and it's your job to go, watch this, I will make it work.' Now, in his mind, he knows Phil's reasons for everything he does: 'It's Phil's world and it all makes sense from his point of view.'

Except Phil himself has changed. Once the decent straight guy to Grant's selfish thug, Phil Mitchell has become, over the last year, Walford's Nasty Git. But McFadden understands why. Phil's been had over by a lot of people, so now he feels like he can do it back. It's his history. Soap stars carry a lot of it. Which McFadden enjoys: 'A flick of an eye at the appropriate character is meaningful, when you've had five years with that person. It's one of the most underrated aspects of acting on a soap. When I was at drama school you'd do these exercises, and this is like a 10-year exercise for me of in-depth living of one particular character. It's a luxury.'

Can you see the difference between Phil and Steve yet, viewers? Steve is - and who would have thought it? - a bit of a luvvy. Not in the mwa-mwa-fabulous way, but in the way he analyses and works at his character. Steve is a proper act-or: he went to Rada. And personally, I think - like many of the EastEnders regulars - he's far better than our nation's theatre darlings. You just need to watch Sheila Hancock's recent EastEnders' cameo appearance to see that. Her insistence on wringing the emotion from every single word in a sentence just seemed ridiculously hammy next to the subtleties of Martin Kemp's performance. Out-acted by a member of Spandau Ballet. The shame.

Anyway, McFadden talks like a pro of 'monitoring' when he works, getting the balance between the mechanics and the emotion. 'I don't pretend to cry, there are tears coming out of my eyes. You can't pretend that. If I go red, it's because my body temperature is actually going up and I am actually angry, because I believe you've shagged my wife. You've got all that emotion, which is real, but then a bit inside that is stage-managing.'

McFadden loves all this, he loves what he calls the 'Rubix Cube' of acting. He finds the technical conundrums fascinating - 'How do you breathe in a sentence and where do you get the idea that you say what you say, and how do you make what is written on a page believable and not as though you're just reading it out.' He doesn't see himself as a natural; he says he learnt his craft 'like Lego bricks, one clunk at a time', until now, he's 'got a handle' on it. Now, he knows when he's got it right: when the studio floor goes quiet, when, among all the chaos and grind of everyday filming, other people are silenced by a performance.

Unlike many of the EastEnders ' cast, McFadden wasn't a child actor. He was born on 20 March 1959, in London's Harlesden, to Barbara and Bob Reid. But his parents split when he was two, and he was brought up by his mother's second husband, market trader John McFadden, the man he calls his dad. Steve had no contact with his biological father until late in 1999, when Bob Reid surfaced, in the pages of The Sun. I ask him about their relationship, and he fixes me with a very Phil stare.

'The fact that you ejaculate into a woman doesn't give you the right to call yourself a father,' he says, with some force. 'What gives you that right is being a father. I don't like people saying that my dad [he means John McFadden] isn't my real father, because he is. Just because he didn't ejaculate into my mum nine months previous to 20 March 1959 doesn't make him not.'

McFadden is himself a dad now: of Matt, who's 15, and Teona, three. He's separated from their mothers, but is 'determined' to be a father to his children. He mentions them a lot in interviews, stays in during the week to look after them. Fatherhood, and what makes it, is a recurring feature in his life, what with his father(s), his own children and his job: Phil has a son whom Kathy took away to South Africa, and there's impending parenting complications with Lisa, Phil's ex-girlfriend. Lisa is played by Lucy Benjamin, who is McFadden's girlfriend in real life. They met on the soap and have been together for 18 months.

'When I was a kid,' he says, 'if I was unhappy, I'd stroke my dog. I was into bringing injured birds into the house, RSPCA activities. And the relationship that you have with animals, you can get that from your children: that unquestioning love and adoration and equal need. However the world judges you, if you do your kid two slices of toast for breakfast, you've achieved what you are on the planet to do.'

McFadden himself was an only child, a 'balanced' boy who could be both sociable and introverted, a city kid who liked the country. But he was naughty: he sat at the back in class, and was the best fighter in his year: 'It was a rough school: that sort of stuff was more important than the academic stuff.' He didn't read a book until he was 18. 'I didn't know my A to Z until then,' he says. 'I'd learnt it at primary school and just never learnt it properly, it never sunk in.'

By 15, despite his parents' strictness, despite his own vague liking for Geography and English, Steve's main concern was being a powerful figure in his gang, 'not being taken for a mug'. Sometimes he looks at groups of teenage lads and thinks of himself. 'I think, that's a right bunch of tearaways looking for trouble, and that's what we were. You don't think, there must be some soul who wants to break out and become a thespian.'

But McFadden was that soul. When he left school, he did some labouring, plumbing, worked at a builder's merchants, helped his dad out. Nothing really clicked. So he sold his motorbike and hitchhiked around Europe, settling for some months in Montpellier. He slept outside on land earmarked for development as a football stadium. It reminded him of the freedom he enjoyed on holidays at his granny's in Norfolk, where he used shotguns and catapults, rode motorbikes at 12-years-old. When he came home from Montpellier, he'd changed. He slept in his parents' garden for months. London had become too repressive, too inner city for him. McFadden needed more.

So he went to a Job Centre and said, 'I want a job with meaning.' He ended up working with blind people, on a scheme called the Acorn Project. Part of the scheme involved going to college. He stayed on and got his O levels, then his As, in sociology and politics. Next step was North London Poly.

At the same time, McFadden was getting in trouble with the police, for smoking dope, burglary and fighting. What were you up to?

'It was just what I like to call high energy,' he smiles, though he clearly doesn't want to give much away. 'There was a bit of gang warfare going on, very unpleasant at one stage. But I fought with strangers as well, I wasn't fussy. It was: Friday night, let's have a punch- up, Monday morning, let's do my degree.'

And then, seven weeks into his degree, McFadden was sitting in his economics class, looking out of the window, 'at guys pulling bricks up to the scaffolding the same way they used to do in medieval times. And I thought, I don't want to be a medieval brick hauler. And I don't want to be a 20th-century pen pusher. I'd really like to act.'

He says it was a genuine moment of revelation: 'I felt lighter.' He walked out of class, handed his grant back, and went to Foyle's bookshop. He chose a speech from the first play he pulled out, 'a mad 1960s piece' called KD Dufford, Here's KD Dufford, Tell KD Dufford How to Make KD Dufford by David Halliwell. A friend, Mick Mahoney, football hooligan-turned-playwright, told him about Contact magazine, and McFadden copied out a list of drama schools from that. He was told by Manchester University that he should give up before he started. Three days later, he was accepted by Rada. He was 25. During his time at Rada, he co-opted some of his Kentish Town mates into his own drama piece and won his year's prize for - oh irony - Best Fight.

There are some aspects of Steve's life that cross over into Phil's. Phil hates being taken for a mug; there's the fatherhood thing; the slight suspicion of women (Steve admits to being a 'man's man'); even the alcoholism: Steve's dad had a vodka problem when Steve was a teenager. But they are different. Steve's a lot calmer and more patient, for a start: after a full day's work, he's happy to talk to me for a full hour, and then couldn't be politer when asked to hang around in the freezing lot for photographs. He's generous to others, too: he phones up the following day to emphasise how much he rates the writing on East-Enders, the way the ante was upped without offing half the characters. Steve owns a Rolls- Royce and two boats - a barnacled barge in Cornwall, and a glamour one in Marbella - which Phil could only dream about. And Steve likes a joke, which Phil, well, could only dream about.

It would be nice to see McFadden be someone else for a change. He was excellent as a beleaguered fireman in Murder on the Mind ; his first ever screen performance, in Gary Oldman's hooligan film, The Firm , is great, too. He'd be good on stage - he's got that still, commanding presence of the controlled hard man that would work amazingly in the theatre. We talk about it for a while, but then agree that most theatre is rubbish, not worth his while. So, after a decade in the Square, would Steve like to be in EastEnders when he was 50?

'No,' he says, finally. 'I don't have a time span on it, and I love it, and as long as it's still challenging then I want to be there. But eventually they'll run out of stuff for Phil to do. He could be a priest, I suppose. Vicar of Walford. Rugby tackling people as they go into the Vic, forcing them to the Lord. Still,' ponders McFadden, 'I could do a lot with that...'