He is talking about his recovery on Pearse Street. We are no more than 100 yards from the needle exchange. When he lived in Dublin it didn't exist. He survived using the same 10 needles in an eight-month period.

If you have ever tried to use a blunt instrument to open your skin you will know.

This story is spectacular. It is rags-to-riches rehabilitation. The publishers Little, Brown paid a half million sterling for it. Mark left the street. He now has two businesses, three careers and several consultancies. He is paid by the British Cabinet Office for his views and input and has earned the trust of Prince Charles, who visits him in a palace he passed out behind while injecting. Victoria Beckham presented him with an award. He just had dinner with British Home Secretary John Reid. He speaks with a midlands accent and an innate storytelling ability. He is not on an ego trip, but the opposite:

"All this stuff is self sacrifice.

My mum said: 'Up until you were 29 I always viewed you as my sick son. Towards the end I used to imagine myself at your funeral.

Every time I thought of you I saw myself going to your funeral.

Now you're 36 and going to Clarence House.'

"But that's all on the outside.Public figure stuff. I know it can be more addictive than heroin. All I'm doing is opening a door for people like me. I think that's the reason I cope with it . . .because I know it's not about me. If it was, I would feel pathetic. All I would be is a bloke talking about myself."

When the Prince's Trust handed over �3,000 in 2001 to a man who had stolen many hundred times that amount, they gave him life. He did not steal. He won their Achiever of the Year award in 2005 and collected it from Victoria Beckham.

Johnson's successful business, in tree surgery, employed exaddicts like himself. He had 12 but had to scale down. Life took over the dead man and catapulted him into a position of key influence. Prince Charles has befriended him, trusts him to deal with the issue of reoffence:

"Seventy-five percent of young people re-offend within two years. If we were in the tree business we would be bankrupt."

He'll never be done making people understand, paying recompense, staying well.

Here is why: His opening words in his memoir Wasted talk of his bereaved cells. For years crack heroin kept his real emotions at bay. When he came off it, he experienced 14 years of blocked-out memories after just 14 days of clean blood.

His Birmingham childhood came first. He was beaten and he beat others. He was sexually abused and abused others. He lived with a crack addict who worked as a prostitute and she introduced him to the drug. He was sexually disturbed. He lost his virginity to 14-year-old Bianca at the back of the youth-club hall, after a 10-minute chase.

By 20 he had watched his friends queue up to rape a girl with special needs and had been imprisoned for violent robbery (his second incarceration; his first was borstal for "violent disorder"). The next 10 years were devoted to heroin.

All the time Mark Johnson thought: "It's not me." He is living proof that people are not born brutal. One of the reasons the book is attracting rave reviews is because the voice of the child he was is at odds with his behaviour.

The child is fragile, the behaviour lethal. Why?

His father was a peripatetic steel worker with 'Love' and 'Hate' tattooed across his knuckles. Mark could never differentiate which was which.

"It was easier to love him when he wasn't there, " he recalls. By page 20 of Wasted, which makes Trainspotting read like trainspotting, he has been beaten three times . . . self-harm in detox, once by his mother in church and then a belt attack by his dad. By page 24 he turns six, is drunk on Strongbow and chain smoking.

By 11 he has used heroin. Mark Johnson will never get back what was stolen from him. Or what he stole.

His own child, Jack, was left in his care aged two. Jack saw his father black out with a needle in his arm. What Johnson would not do for heroin. He hid it under his foreskin, in his rectum. He won't hide facts or make excuses for his past:

"That book is me, who I was, " he insists. But there is a proviso.

"Even in the last month I have changed unrecognisably to others and to myself. I absorb life. I was seven years old emotionally when I stopped using. I am picking up now, I'm about 18 years old. I still don't understand what it's like to be in a relationship. I can be so hard."

His recent appointments to the Prince's Trust and the British Probation Service are amazing to him. "It's Prince Charles who did that. 'Of course, Mark, I'm counting on you to deliver this for me, ' he said to me. That was it, the future King of England saying, 'I'm looking at you.' It holds a lot of responsibility but I know I can do it.

"The best person to know these needs is someone like me, " he states. "When you're in front of 500 people, chief of police, director of social services, people who deal with people like me in the dock every day, there is a little part of you that thinks: 'Is this the reason that I am alive?'

I'm not HIV positive and I used to grab needles off people who were dying of the virus. Twenty years of IV drug use and I have clean blood."

In observation I cannot equate this gentle man with one who left people for dead. Mark Johnson was, though never violent, horrific in his neglect of his eldest boy Jack. He used to "throw him sweets in the front of the car so I could inject in the back seat". Both his sons were treated at birth for withdrawal symptoms. You know he suffers with this more than anything.

"I have to tell myself I've been seven years clean and spent a year of psychotherapy on this part of my life alone. All I can say is I didn't know any better. One of them hasn't ever seen me pick up a needle. The other one's memory is fading." You can see his own hasn't. The boys' mother, Rosie, has been clean for three years also. "She's amazing."

The nature of addiction, according to Mark Johnson, is being self-centred. "Everyone in my house was segmented. The walls between each of us were fear. The fear was my dad. When he called me a poof for wanting to go to art college, the rest of the family called me a poof. He was ruler." This was part of the reason he moved out, trying to go to college but ending up in prison. After that he decided to try Ireland to work for a forestry company. Few people wish to climb as high as Mark Johnson.

Few people have fallen as far. The worst experience of addiction was the Dublin experience, for eight months of 1997. "I flushed my supply down a toilet at Manchester airport and got on a plane to make a new life. I thought, 'There's no heroin in Ireland, moving there will get me off it.' The following night I had nicked the works van to score." It wasn't until he arrived that he realised heroin addiction was epidemic and securing drugs was more dangerous: "I was a wreck. I drove from Blessington to Ballymun. When you're a junkie you know where to go."

He knocked at a known dealer's house. "The door opened and two people jumped out, dragged me over to the flats and beat me up. At the time the Concerned Parents movement was trying to stamp out hard drugs. A lot of junkies lost their lives then. I was served by 10year-old kids, on bikes with no saddle, who couldn't be done.

"There was no stability in my sourcing so I had one batch to last me weeks and weeks. I got sick, very sick, living here. I got arrested. When I arrived in the police station they couldn't believe my story, that I was a junkie. I was given an internal search. They thought I was a member of the IRA. Why would an Englishman emigrate to Ireland and score when he could lose his life doing it?"

Two years later he got clean.

His redemption takes 20 pages of his book, but he has eight inches of diaries on the subject. Gore, desperation and horror sell but redemption is what this man is all about. From his last fix, in July 2000, to today, he has been fixing himself perpetually. Now he will help others. How does this square with seven years ago?

"It doesn't. It blows your mind. All the policy and law-makers involved in prison. The weird thing is I know what I'm talking about." Do they? He shakes his head. "No. I talk in government think-tanks and in other highlevel meetings. I've written papers. They still don't know what I'm talking about.

"People that make policy predominantly cannot comprehend the lack of choice most offenders have, from birth.

Huge f***ing holes missing. I had dinner with John Reid and he said it's popular to send people to jail. I said, 'Let's make it unpopular!' I'm now sitting on the Offender Management Team for the Home Office, the Cabinet Office give money to the OMT, who disperse money to all the services for ex-offenders."

Johnson is surrounded by gravestones and his should have been one of them. He feels there is a higher power because the fact he is not HIV positive, or buried by now, is more than unusual . . . it is miraculous. As is the establishment turning to him.

Is there a danger it will use him only as a talisman?

"Sure. It's a racket . . . but I know I am there for a reason. I told them: 'You don't know what you're letting yourself in for.' I am entwining around and through them. There are massive things I have in mind. I told them: 'Be careful what you wish for.'" 'Wasted' by Mark Johnson is published by Sphere, /20