Noel "Razor" Smith looks like a man with a serious past. His shaved head, clipped goatee, steel-blue eyes and thick-set shoulders give him an appearance that epitomises the popular perception of the heavy villain. But Smith doesn't just have the look - he has the CV to match. His criminal career began when he was barely into his teens and should have peaked when, aged 16, he appeared at the Old Bailey on multiple charges of armed robbery. Instead, after his release from the resulting three-year detention order (the judge said his crimes warranted a sentence of 14 years but decided to give him a chance because of his youth), he embarked on a way of life that could only be described as an all-out war against the police and society at large.

As a young Teddy Boy he carried an open razor and lost no sleep over using it on rivals during gang fights. While his passion for guns grew, inevitably his criminal acts escalated. By his early 20s he had developed into an armed robber who gave no quarter. Looking back, he says he was "a lazy, greedy bastard" who had no interest in working for a living and that he came to live for the "buzz" of professional crime as well as the spoils, which, when he was not in prison, provided him with a lifestyle of flash cars and luxury flats. In one pub used regularly by Smith and his gang the unsuspecting landlord, impressed by the smart-suited men who made a big deal of breaking £50 notes, called them "the four yuppies".

Following a series of pre-Christmas bank raids one year, during one of which the gang wore Santa hats over their ski masks and cracked jokes as they filled their sacks, the Flying Squad gave them another name: "the laughing bank robbers". Now aged 44 and almost six years into eight life sentences - all for armed robbery - Smith is no longer laughing. And his appearance belies the now calm, reflective man within.

We meet on the ground floor of Smith's wing in HMP Grendon, a high-security prison which offers those in its custody a specialised therapeutic regime. It is not an easy option. Offenders have to face up fully to the consequences of their criminal actions. I wondered whether, after a lifetime of wrongdoing, the choice to come here had been a difficult one. "I was wavering for a while," he says, "but when I actually made the decision it was liberating. It was like getting out."

During prison sentences through the 80s and 90s, before he got "lifed off" in 1999, Smith had a reputation for instigating exercise yard sit-downs, persecuting sex offenders, assaulting prison officers and plotting escapes. In prison parlance he was "staunch". I'm curious to know if he misses the hard-core prison culture.

"Sometimes I get letters from people in Long Lartin, Whitemoor or Frankland [three of the highest-security prisons in the country] and I get a little twinge of I'd really like to be back and part of that. But it's strange. I'm sort of on a journey at the moment. That might sound a bit pretentious, but that's what it is. It started from the moment I came here. In the last four months I've started to get a handle on it and I can see that it really does work. It is really weird. It's hard to explain."

The reason we're talking is that Smith is about to release his first book: A Few Kind Words and a Loaded Gun - The Autobiography of a Career Criminal. It is an extraordinary book - not just because it is a highly literate debut which chills and thrills in almost equal measure - but because when the author first entered the adult prison system he could barely read or write. Yet, self-taught, he writes in prose that bristles with confidence, with an honesty that is rare in the criminal memoir.

So why did he veer so far to the other side of the tracks? A clue lies perhaps in an event which occurred when he was just 14. While playing truant he and a friend were stopped one day by a vanload of plainclothes policemen. The officers dragged the two boys into the back of the van and accused them of burgling houses in the area. Smith says they had no knowledge of any house break-ins. He says the police gave him and his friend a beating in the van that "amounted to torture". In an effort to make him confess, one officer twisted one of Smith's fingers until it broke. Magistrates later threw out charges against the boys and called for an inquiry into the behaviour of the police. An investigation was launched but fizzled out. Noel Smith never forgave.

At the height of his criminal career Smith and his gang were robbing "an average of two banks a month". I asked him if he ever considered how his actions affected the people he robbed. "You've got to detach yourself. So you tell yourself you're a Robin Hood figure. If you sat down and told yourself the truth: I am a nasty, violent man, going out there and terrifying innocent members of the public in order to steal money because I'm too lazy to go out and work for it, you'd never go out and do it. So you cut yourself off."

His writing activities began as part of a business enterprise while he was in Albany prison on the Isle of Wight in the 1990s. An associate made greetings cards to sell to fellow prisoners. Smith, who was writing poetry "to try to win the prison's annual Christmas poetry competition", would write the verses. "I haven't got a clue where that came from," he says. "It was just something I could do."

It was something he could do well. Later he entered outside poetry competitions and won several large cash prizes, including one runner-up prize of £750 from Raconteur magazine. He began contributing to a magazine called Prison Writing. Former armed robber turned author John McVicar, who was on the editorial board, took an interest in Smith's writing. "John showed some of my short stories to a friend of his called Will Self, who I'd never heard of, but he liked my stuff and we began corresponding."

Smith met up with Self after he was released and there was talk about him earning a living from writing. But it wasn't long before Smith was once again waving guns in people's faces. When he was finally arrested it was bad news for Smith the robber, but Smith the writer got another lucky break. Soon after his remand to Belmarsh, ex-cabinet minister Jonathan Aitken, who had been sentenced to 18 months for perjury, landed two cell doors down from Smith in the bleak London prison. The two men became acquainted and Aitken agreed to be interviewed by Smith.

"Aitken surprised me," he writes in his book, "He seemed to settle in very quickly and comported himself with bravery and dignity. He didn't ask for any favours and showed courage by not asking to be put on the protection wing." The interviewappeared in Prison Writing and McVicar sold it, on Smith's behalf, to Punch magazine.

In spite of the time lapse since their brief time as neighbours, Aitken has not forgotten his erstwhile interviewer. "It would be hard to find a tougher man on a prison landing than Noel Smith," he says, "yet I also found him to be one of the gentlest and kindest I could have wished to meet."

The interview was a success but Smith was a long way from writing his first book. Then tragedy struck. Two years after he received his life sentences, his 19-year-old son Joe hanged himself. He had just finished a stint in Feltham Young Offenders Institution. Did Smith feel some responsibility for his son's death? "Massive responsibility," he says. "Every day I still do." A Few Kind Words is dedicated to Joe. "He wasn't a strong kid," says Smith. "I think he was worried that his life was going to turn out like mine and I don't think he could have handled that ... After Joe's death I felt I needed to leave something behind, so that my family might have some understanding of my life."

The book was written after some encouragement from Self, who acted as Smith's agent: "I think he has a unique voice and could evolve into a significant writer," he says.

When the time comes for me to leave and we are shaking hands, I ask him what he would like to do if he ever gets out. He thinks for a moment. "I'm at the stage where I'm not in any hurry to get out. When you do short sentences all you're thinking about is out, out, out. I don't feel that now. For me now, the perfect life would be to get out eventually, obviously, and just have somewhere to live and somewhere to write. And that would be ideal for me."

· A Few Kind Words and a Loaded Gun - The Autobiography of a Career Criminal is published by Penguin next month.