By ANGELA LEVIN

Last updated at 22:58 12 January 2008

With his prominent cheekbones, ice-blue eyes and an unmistakable hint of mischief, the family resemblance is clear enough.

But while his sister Lily is internationally famous as a singer and his father Keith is one of the country's best-known hellraising comic actors, few people have yet come across 21-year-old Alfie Allen.

If you have heard of him at all, the chances are it is through Lily's hit song Alfie, which described him, to his horror, as a pot-smoking layabout with the affectionately mocking words: "My little brother's in his bedroom smoking weed, I tell him he should get up 'cause it's nearly half-past three."

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As a wild-child who was expelled from school after school during his formative years in North London, Alfie admits that Lily might have had a point.

But today that little brother is sitting in a spartan canteen.

He is taking a break from a punishing schedule of rehearsals and warming his hands on a small bowl of green pea soup and a cup of herbal tea. He is a picture of concentration.

After 21 years playing a bit part in the lives of famous adults - including comedian Harry Enfield, a father figure at a crucial time in his life - Alfie has found a role of his own.

He is about to take on his first leading part as the troubled, horse-obsessed character at the centre of Peter Shaffer's play, Equus.

And his film career is also blooming.

Next month he will appear on the big screen in Flashbacks Of A Fool with Daniel Craig, and in March he will be seen in The Other Boleyn Girl, a movie starring Scarlett Johansson as Mary (a rival to Anne Boleyn for the hand of Henry VIII).

It might seem that Alfie was born to success, a member of the media aristocracy with a celebrity father and a film-producer mother.

The reality is rather more troubling. By rights we should be talking in a therapist's consulting room or perhaps in The Priory clinic, where Lily spent a brief spell.

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Because if Alfie has inherited the family gene for success, he is also prey to its demons.

When theatre audiences see him play Alan Strang, the creative yet disturbed anti-hero of Equus, his own troubled psyche will also be on view.

"I have to keep the lid on myself," he admits, speaking for the first time about his fractured upbringing and a father who notoriously finds it hard to adjust to conventional demands.

"I have to work hard to be punctual, to not lose my temper, take direction and be told what to do - and most of all listen rather than talk.

"Although I have fantastic connections, I didn't know as a child what feeling secure meant."

His upbringing, marked by explosive outbursts, expulsions and visits to psychiatrists, could have sent him off the rails for good.

Yet his childhood has been redeemed by strong relationships with the very adults he could have blamed and turned against for ever.

To understand why someone with such a seemingly privileged background should have to struggle in this way, it is necessary to travel back to the well-appointed streets of Primrose Hill, where he grew up in the Eighties - and perhaps further back to the time when his colourful but talented parents first met.

Keith Allen has left him with quite a legacy.

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He is one of our most celebrated performers, currently starring as the evil Sheriff of Nottingham in the BBC's Robin Hood series.

Yet, expelled from almost every school he attended, Keith was sent to borstal for theft, then to prison for smashing up a bar in the West End.

He has fathered half a dozen children by four different mothers.

Does Alfie feel they spend enough time together? He shifts uncomfortably in his chair. He is protective of his parents, particularly his hard-drinking father.

"I really don't like talking about my dad," he replies slowly.

"I've always known my dad is a one-off and his own person. But I feel that underneath he has always loved me.

"He is the best dad in the world in many ways, as well as the funniest person you could meet.

"And when you really, really need help, he's always there."

The true constant in his life, however, has been his mother, Alison Owen.

She has been a rebel in her own right, too – a single mother at the age of 17 and a punk when she met Keith at a music gig in Notting Hill.

She has also been successful, albeit behind the scenes rather than centre-stage.

In 1998 she produced Elizabeth, which starred Cate Blanchett and for which she received an Oscar nomination, and last year she produced Brick Lane, the film of Monica Ali's novel.

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She became Keith's first wife in 1984.

She already had Sarah, now 27, and more children soon followed. Lily was born in 1985.

Then, not long afterwards, Alfie was conceived on the banks of the River Yangtze in China.

Another famous name was soon to enter Alfie's life, however. After seven years of Keith's chronic infidelity, his parents split, and his 32-year-old mother moved in with Harry Enfield, a friend of Keith's, who was then at the height of his fame as the vulgar Loadsamoney character.

Alfie was five. He remembers Harry, 33 at the time, as extraordinarily generous.

When Keith ran into trouble with the taxman, saying he owed £75,000 and that he couldn't afford to pay the children's £15,000 school fees, Harry paid them himself.

Harry and Alison lived together for three years and a wedding was planned for 1995, at which Alfie was to be a page boy and Lily a bridesmaid.

To outsiders it seemed the perfect match, but in July 1995 the couple split. Harry was said to be heartbroken.

"He adored us and we adored him,£ says Alfie.

"I call him my stepdad even though he wasn't quite. He was my father figure for quite a while.

"He's a lovely, funny man and I love him to bits. His biggest influence on me has been to give me my silly sense of humour.

"We still see each other. We met for a meal just before Christmas.

"I took my girlfriend along to meet him. She said afterwards that she could definitely see him in me, especially his humour."

But even Harry's influence was not enough to keep Alfie on the straight and narrow.

His behaviour deteriorated after his parents split and he began to do badly at school.

With all the adults in his life working hard, he was cared for by a series of nannies – another unsettling factor.

"There were loads of them because all three of us were hard to handle," he recalls.

"Not many lasted very long and some were a nightmare.

"One Australian nanny loved drinking Jack Daniel's and another from Yugoslavia made us bathe in about an inch of water because she said that's what they did in Yugoslavia."

Like his father, Alfie was expelled from a series of schools, both state and private.

Lily suffered a similar fate, attending more than a dozen schools before leaving at the age of 15.

Two years later, she spent time in The Priory with depression.

"There wasn't a lot of discipline in my life and I hated it being imposed on me at school," explains Alfie.

"I wasn't expelled for anything vicious, just being cheeky, not doing what I was told, answering back and always rising to the bait if someone said something annoying about my dad.

"My mum was very upset each time it happened. She always called Dad and said, 'Be angry with Alfie.'

"My dad would arrange to see me and say, 'I'm going to be angry with you.'

"But, to be honest, he didn't really know what he was being angry about."

Desperate for a solution, his mother sought medical help and Alfie found himself diagnosed with Attention Deficit Disorder, or ADD, and became one of the first children in Britain to be prescribed Ritalin, the controversial drug said to help improve concentration and control hyperactivity.

"I hated it," he recalls. "Soon after I started taking it we went on a family holiday to Ibiza.

"I'd never been a reader but all I wanted to do was stay in my bedroom reading a 400-page book on King Arthur.

"My mum said it wasn't me, and got me off Ritalin as soon as we got home.

"My dad was always against it, but my mum wanted to give it a go."

The next attempt to curb him was more dramatic still.

At the age of 12, Alfie was sent to a "boot camp" in Fort Lauderdale, Florida, under the care of a leading child psychiatrist.

This time the results were positive. "It was a turning point and really sorted me out," he says.

"I had to share a room with a boy about my age who I still hate with a passion whenever I think of him.

"The psychiatrist told me she chose him as my room mate because he was almost a mirror image of me.

"I thought he was a spoilt brat. Initially I was angry with him all the time, but being forced to live together meant I had to teach myself to keep my cool and not lose my temper. It's stayed with me.

"My mum came over for sessions with the psychiatrist, too, because she felt it was her fault that I was like I was.

"I disagree with her. I believe I was born angry, but I'm pleased that the time I spent over there worked."

Well, not entirely. He went on to be expelled from his final secondary school, St John's College in Southsea, Hampshire.

Alfie is devoted to his mother. "I still live at home and think she is such a great woman," he says.

"I've learned determination from her. It's incredible that at 17 she had a baby and lived on her own in Portsmouth and still managed to become an Oscar-nominated film producer. I am so proud of her.

"I have no complaints about my childhood. Once I started to grow up I realised that my parents are normal people and they can make mistakes.

"If anything, my experiences as a child and the problems I've been working so hard to overcome have helped me understand my character in Equus and play him with a much deeper conviction.

"I've got rid of the ADD but I do find it hard to concentrate sometimes.

"The difference is that I didn't want to learn at school, but I am enjoying this so much and want to do it well."

Alfie says there was no family pressure on him to become an actor.

Just as Lily had wanted to be a musician from an early age, he had always wanted to follow the example of his father.

"My dad was annoyed about that," he recalls. "He was keen on me doing something sporty as I was good at rugby. I chose not to because I loved going out too much.

"Ironically my dad is the reason I wanted to be an actor.

"I saw him having fun and always doing impressions and sketches.

"He was so cool and I wanted to follow in his footsteps."

Alfie had planned to attend drama school but was offered a part in Stoned, a film about the late Rolling Stones musician Brian Jones, before that could happen.

He was quickly noticed, going on to play Danny Hardman, the gardener's son, in Atonement, the film of Ian McEwan's novel.

"A lot of people have the misconception that I decided to become an actor when Lily became famous and have accused me of jumping on her bandwagon, but that's completely untrue," he says, denying that he feels in any way overshadowed by his sister.

"We get on brilliantly and I am immensely proud of her."

Lily, 22, is pregnant by her 37-year-old boyfriend Ed Simons, one half of The Chemical Brothers club music and DJ duo.

"She's at home in bed today and everyone is running round looking after her," laughs Alfie.

"Mind you, you have to look after Lily even if she isn't pregnant."

He's even forgiven her for writing the disparaging song lyrics. Was she telling the truth?

"All sisters exaggerate," he smiles. "Let's say that elements of it were true, but it concerned a part of my life that was private and I didn't want people to know about."

He beat more than 200 actors to get the part in Equus and is now throwing himself into the rehearsals.

"It's an amazing opportunity and I'm going to grasp it. I'm trying to be really professional.

"I've given up clubbing until the end of the tour in June and most evenings I don't go out at all.

"Just before New Year I also gave up smoking. It's very, very hard but I know it's good for my throat and, of course, my voice."

Alfie says he is not intimidated by following on from Daniel Radcliffe, the Harry Potter actor, who played the part before him.

"I didn't see him in it and I expect I shall do it in a different way," he says.

Joining us during the interview is Alfie's Dublin-born co-star Laura O'Toole.

Laura, 22, and Daniel, 18, have been an item for some months after meeting on the set of Equus but with a four-month tour looming they have decided to cool it a little.

"Daniel and I are still good friends and have a good time when we see each other," she says, blushing slightly.

"We just have to be realistic."

Equus is a particular challenge because both leading actors must appear naked.

Laura and Alfie have already had to strip off together for publicity shots.

Was it sexy? "No, bloody cold," laughs Alfie, who is dating Jaime Winstone, daughter of actor Ray, and doesn't seem in the least bothered about stripping.

"I enjoy any excuse to whack it out," he jokes.

"And you can see me nude again in Flashbacks Of A Fool."

Is he nervous about what the critics might say or will he take his father's bloody-minded approach to popular opinion?

"I care what people say if I know the person saying it loves me," he says.

"If they don't, **** them. Sorry for swearing. But I'm not doing this to prove anything to anyone but me."

• Equus will be on tour for 16 weeks starting in Chichester at the end of January. Anyone under 26 can buy any seat at any performance during the entire run for £10. This has been made possible by the Arts Council.