Ten years ago Mark Johnson was down and out in Dublin with a deadly drug habbit. Now he's an adviser to the Prince's Trust. Kate Holmquistreports on his decade of upheaval

'Living is only for what hits for me now. I'm like a fairground machine. Put in some money and it's all lights and colours and music. The money runs out and it stops." Drug addiction ran Mark Johnson's life from the ages of 16 to 30. He stole, dealt drugs, beat people up, recruited prostitutes and used people to get his drugs - even a suicidal Japanese woman who paid him to get cyanide.

"When you come from dysfunction, your world is very narrow. You only see an alleyway ahead. There are not the same choices as with someone who's had a healthy upbringing," he says, now seven years "clean".

Currently an adviser to the Prince's Trust and the UK probation service, Johnson has written a first-person account, Wasted, of what it's like to grow up in an abusive home, then turn to heroin and crack to ease the pain.

When Johnson was living in Dublin nearly a decade ago, he furtively bought heroin from 10-year-olds on bicycles in Clondalkin, Finglas, Ballymun and Fatima Mansions, shot up behind bushes to hide from the "concerned parents", then went to work as a tree surgeon.

Pumped with the heroin he used to fill his inner void, he shimmied up tree-trunks with a chainsaw in the forests of counties Wicklow and Kildare. At night he "stole" the firm's truck and drove in search of more heroin, with a group of heroin-hungry passengers from various walks of society riding in the back through areas so dangerous that he would drive slowly, but never come to a complete stop, in order to avoid being beaten up.

He was 28 years old and resigned to always being an addict. "You think you can control it by using just enough heroin to stay 'well'," he explains, "but the consequences of having to constantly find and pay for more drugs escalate rapidly until life is completely chaotic."

Living in Britain, and having worked as a tree surgeon at No 11 Downing Street, among other places, he came to Dublin when he could no longer get work in the UK. He survived for nine months in Dublin with a packet of 10 needles that he managed to con from a chemist by convincing her he was diabetic. He used those needles until they broke, then he used half-needles so blunt that his vein jumped to either side of the needle when he tried to inject, which he succeeded in doing even though his arm was covered in blood and he was crying in pain. He left Dublin when heroin - which cost four times more than in the West End - became too hard to get, partly due to the actions of concerned parents' groups.

By the age of 30, he was down to less than eight stone (50.8kg), with body lice and scab-encrusted feet, yet was willing to endure anything to get a fix - which cost him €150,000 per year. When waiting for his fix, he ached and burned and his nose ran. He sat in tower block apartments with 20 other addicts while children in nappies ran around.

Flip to any page of Wasted, and you will find intense pain, bottomless need and wilful self-destruction - all described without a trace of self-pity. Now the owner of a successful tree-surgery business that he started with a grant from the Prince's Trust, Johnson is on a mission to educate the public and policy-makers about the realities of the addict's life.

He won the Young Achiever of the Year from the Prince's Trust and went on to receive the Daily Mirror's Pride of Britain Award from Victoria Beckham.

He has spoken at length with Prince Charles about what needs to be done to save young people from drug addiction, and found the prince to be an intelligent listener who was convinced by Johnson's argument that the very services set up to "help", "treat" and punish drug addicts in the UK are making the problem worse.

Prince Charles has been an inspiration to him. "I'm counting on you to get this right," Prince Charles told Johnson, who says: "No one will ever know what that man does for people . . . his attention to detail is unbelievable. Without Prince Charles, I would not be here." Johnson is now running a pilot scheme for the Prince's Trust that involves young offenders being mentored by ex-offenders who have turned their lives around. Johnson is also the first ex-offender on the board of the National Probation Service.

"TWO-THIRDS OF young offenders reoffend because the people making the decisions don't understand the problem," says Johnson, who was so traumatised by his first experience of prison - stripped naked and beaten up by seven guards - that he began using heroin again when he was released in order to deal with the pain. Within two months he was back "inside" doing time for a violent robbery.

Johnson wrote Wasted after a literary agent read an article he'd written in the Big Issue and approached him with a book deal. The book is a remarkable account of how a child of eight from a seemingly banal background starts drinking, uses "entry level" drugs at 11 and is a heroin addict by age 16. "As soon as I used heroin I had that sense of arrival, it filled the hole in the soul," he says.

Children and young people use drugs like heroin when they have never experienced love in the way they were supposed to. He says, "The drug fulfils the need for love . . . It's a painkiller, it's beautiful, euphoric."

Johnson's mother was a Jehovah's Witness with extreme views and his father beat him up on a regular basis with fists tattooed with the word LOVE on one hand and a cross on the other. From the age of about eight, Johnson was sexually abused by an older schoolmate whom he was powerless to fend off. The stifling, punitive atmosphere at home made it impossible for Johnson to confide in anyone, since telling them about the abuse would merely confirm, once again, that he was "bad".

So he turned to a group of punks in a squat to help him make life bearable and smoked heroin for the first time, though he didn't know what it was.

At the age of 16, Johnson entered art college and smoked heroin for the second time, which is when it took hold. By 17 he was in prison. A life without drugs became unthinkable and he regularly used heroin, opium, amphetamines, acid, cocaine, magic mushrooms, hash and - his old friend - alcohol.

When he moved on to using crack, at the end of the 1990s, Johnson became so obsessed with the drug that when he wasn't in the midst of a high, he was actively seeking one out. In one binge, he became so paranoid that he swallowed 30 bags of crack to keep them in storage, then used them one by one as he defecated them out on to black bin bags. He then traded some of the bags for heroin, which he used to calm himself down from the frenetic, paranoiac high of crack.

He writes, "My paranoia reaches beyond psychosis, it threatens to consume me. I know this is an overdose in some deep-down, long-ignored, rational part of my mind, but I'm still injecting, two at a time, holding onto the sink to vomit, throwing up drugs, shitting drugs. I lie on the bed . . . Crack is in my mouth, it's in my arse, and from time to time I can feel the bags exploding in my stomach, my whole body is exploding with cocaine while I watch the shadows, watch them, wait for them, hear the voices . . . Crack is everywhere, all over the floor, the sink, the bed. It is the Mad Hatter's crack party in here and I'm too weak to move and the heroin rattle is biting into my soul."

Near death, he ended up in hospital, then a rehabilitation centre for 10 months, where for the first time he learned why his brain needed drugs to cope. "The core issues, the fundamental emotional problems have to be addressed. Addicts have a huge piece of their lives missing, so treatment needs a psychological approach," he says.

"Drug addiction is as serious as cancer - in some ways it's worse because with cancer you can grieve, you can get treatment. With drugs the victim is stealing off you, not looking after his kids, lying to you - it makes it easy for you to reject him." He believes early intervention with children and young people at risk is key to preventing addiction.

Johnson insists his objective in writing this searingly honest book was to "open the door" for addicts and non-addicts alike to understand the issues. "If you believe in a higher power - maybe I was led to do this. It's not like I'm a pop star. What I've had to do - speaking in front of police and probation officers - has been really uncomfortable for me." He admits that he could relapse at any time. "I live 24 hours at a time and I take each day as it comes. That's how I find peace."

Wasted by Mark Johnson, is published by Sphere, £11.99