He was expelled at 13 and sent to a home. Now he teaches kids about the Romantics. Just don't call Benjamin Zephaniah cool, writes Emma Brockes

Dreadlocks aside, Benjamin Zephaniah is almost spookily unhairy. He doesn't have to shave. Plucking at the skin on his arm and holding out his hands ("girl's hands!"), he says in his incredulous Birmingham drawl: "I didn't grow pubic hair until I was 21." It enables him, at 46, to preserve an illusion of youth that would be creepy in other men. In Zephaniah it is just part of his dopey persona: he still rides his bike like a boy, bum in the air, weaving up and down the pavement with the kids in his east London neighbourhood. Out of a window last week a woman told him off: "Benjamin, you're a revolutionary poet - you should know better!"

There is, of course, a small but vociferous number of people who find Zephaniah genuinely offensive. His refusal of an OBE earlier this year inspired a run of articles hinging on the word "gratitude" and on the implication, unspoken, that he owed slightly more of it to his elders and betters than the average white Briton did. He has been labelled haughty and annoying. Zephaniah talks about the "oppressed", about the failures of socialism - "they want us all to be equal, but they want us all to be equally poor" - with such unfashionable zeal that even Trevor Phillips, chairman of the UK Commission for Racial Equality, has invited him to grow up and join the "real" world. The poet replies that this isn't his job. Zephaniah's revolution seems to involve running into the room, yelling "Knickers!" and running out again.

I meet him in a room above a bookshop in Newham, the area where Zephaniah has lived since moving down from Birmingham as a young man. "If you want to write about working-class people working hard in a working-class place, that's Birmingham," he says. "I love it. It has some beautiful places. Aston Park. Aston cemetery. Aston Villa. Heah, heah, heah. And I love the accent. Have you ever made love to anyone with a Birmingham accent?" No, I reply. "It's f***ing good." He laughs, wide and deep.

Zephaniah has written his third book for teenagers, a novel called Gangsta Rap, which he says "tells it like it is". His writing style derives in part from the tradition of Jamaican oral poetry, which he listened to on records while growing up. There is a crossover with rap, or "toasting" as he called it when he was young, and his work has been influenced by his dyslexia, which made it easier for him to write down words as they were spoken than as he learned them from books.

Like the protagonists of his new novel, Zephaniah was expelled from school when he was 13 and, after being convicted of burglary, was sent to a residential school for young offenders.

"I felt like a pretty intelligent kid," he says. "Certainly, when it came to dealing with the world I was a lot smarter than, probably, my teachers. I wasn't good at writing maths down, but I was good at seeing maths. I knew when something was out of place. I had a great eye for things. But no one ever came to me and said: 'What do you want? How do you see things?' I once said to my English teacher, 'Miss, do you like poems?' because I wanted to show her mine. And she went, 'Ugh, no. I just do them because it's part of the English course.' So I put my poems back in my pocket."

Education is Zephaniah's big thing. On school visits he reads the kids Romantic poetry and asks them to locate it within the framework of modern music lyrics. "We might have a discussion in which a kid says, well, I think Keats would be like a Morrissey figure, moaning and groaning about how ill he is. And Shelley would be like Jagger, smashing up hotel rooms, and Byron would be like the misogynist, like Eminem, with a limp, hee hee. I'm trying to get the kids to think how to be poetic. Or I might say to them, you're a bad motherf***ing gangsta rapper and you're in love with this bitch. Now I want you to write a poem without using any of those words. And don't use the word love. Simple things. They're not academic. They're instinct."

Zephaniah doesn't mind kids seeing him as cooler than their regular teachers. He does mind being seen as cool by adults, however, sensing an air of condescension that often attends praise of his work.

Before accepting a literary award or honorary degree, Zephaniah asks the panel why they are giving it to him. If the word cool comes up - as in "we thought it would be cool to have you on board", as one university (he refuses to name it) told him - he rejects them. "The way I write, the way I see the world, is part and parcel of my dyslexia and my getting kicked out of school, and I get people coming up to me and saying, 'Oh, you left school at 13 and you're dyslexic and you have 10 honorary doctorates and isn't that wonderful! That's so cooool!' Yeah, really cool to be black and oppressed, innit, so you can write all those angry words." He frowns, then rolls his eyes and laughs; his attitude to life in miniature.

The detention centre, what would now be called a pupil referral unit, that Zephaniah was sent to at 13 was in Shrewsbury, near the Welsh border. He got into pickpocketing and burglary because, he says, he needed cash to keep him in cups of tea and turns on the slot machine.

On his first day at the unit a fellow inmate warned Zephaniah about one of the teachers. "He said, you're going to have a test by this guy, and at the end of it he'll move over to you and put his hand on your knee, and he'll say if you ever have any problems come and see me. And exactly that happened. We spent most of the time - not so much us but the white boys . . ." He tails off. "They never used to touch the black kids for some reason."

What, there was abuse? "Yes," he says. "Sometimes in the night you'd see a little kid get up and go, attending to one of the members of staff, and then he'd come back half in tears." Was there a scandal about it? "There was, years afterwards. Someone grew up and complained. I saw it on TV and was like, I knew that guy! There were different members of staff who had different techniques. A lot of these kids didn't have parents, and if they were shown some affection they - I was going to say 'allowed', but that isn't the right word - they were easy to abuse."

But he escaped; more than escaped. We return to the subject later, and he says again how lucky he was. "Very lucky. I mean, I had an affair with one of the staff." I make incredulous noises. At what age? "Thirteen, 14. I was bonking this woman. So when they wanted to kick me out, I wanted to stay in."

Eventually, he got an education at night school. He moved to London. He got married, then divorced. He could live with someone again only if they "were exactly like me", he says, laughing. He hasn't mellowed at all. Zephaniah goes on a long rant about Tony Blair and the war in Iraq. He talks about his disappointment in Britain's black politicians. "I think there are some white politicians who have done more for black people than some black politicians."

I ask why he's so critical of black politicians; doesn't he think that, while they number so few, it's almost impossible for them to be representative?

"I don't think it's about numbers. I think it's about commitment from individuals. I think if all the black politicians now just dropped dead, hardly anybody would mourn. Nothing like their mourning for Bernie Grant [the late Labour MP\]. Not from the black community. The suffragettes was never a big mass movement. It was quite a small group of women, but they were dedicated."

I ask what he is reading at the moment. "Chomsky," he says. "I am always reading Chomsky." I tell him I find Chomsky hard work. "Really?" he says. "Really? That's cos you ain't got a Birmingham accent." And he throws back his head and brays like a donkey.

- Guardian service

• Gangsta Rap by Benjamin Zephaniah is published by Bloomsbury, £5.99 in UK