Shane Taylor stood in the middle of the road, staring, dazed, at his hand. It was clasped around the handle of a knife, the blade broken clean off. He glanced up. The cars and buses all around him had stopped in their tracks. His friends were looking on, ashen faced. A man stumbled forwards screaming, the knife blade protruding from his eye socket.

Hours earlier, the day had begun in typical fashion. "On the mooch", as Taylor recalls, trying to sell some stolen electrical goods in Hartlepool.

It was 2000, he was a powerfully built 19-year-old and already a hardened criminal, enjoying what he had longed for since getting bullied as a child: a fearsome reputation. "I used to have a motto," he says. "I used to think, 'If anyone ever beats me, I have to kill them.' Life was all about your name."

Around 2pm, he and his friends had chanced upon another gang, and asked if they wanted to buy a video player. But the other gang weren't in the buying mood. Their leader - who was newly out of prison - produced a hammer from his pocket, the kind used by workmen to break paving slabs, and tried to take the video player by force. Taylor ran to a friend's house to fetch a kitchen knife.

I used to have a motto: If anyone ever beats me, I have to kill them. Life was all about your name (Shane Taylor)

Minutes later, Taylor's posse was back on the streets. Their target had moved on to the town centre, so they tracked him down and jumped out from a side alley. "Don't think you're stealing from us," Taylor growled.

Suddenly, there was the hammer again. It came cracking down on Taylor's head. He saw sparks, but he wasn't out cold. He reached for his own weapon, and swung the blade into the top of his assailant's skull.

So now, here he was, standing in the middle of the road, trying to make sense of the results. They weren't quite what he had expected. Not only was the guy still standing, but he was also dragging the blade slowly out from where it was lodged, blood fountaining on to the tarmac. He pointed it at Taylor.

Suddenly, a cry went up: "Police!" Taylor fled.

In the weeks that followed, on the run for attempted murder (astonishingly, the knife attack wasn't fatal), an immediate priority was money. He tried selling some ecstasy, but a rumour went around that they contained heroin, so nobody would buy them. Fed up, he went to a pub in nearby Peterlee to give them to his friends. Also drinking there that night was a "local hard man" in league with a family that had a vendetta with Taylor over a recent alleged kidnapping. The pair caught eyes, and the man approached. "You want to mess around with the big boys, do you?" he said, squaring up to Taylor. Everyone in the room was watching. To protect his name, Taylor reasoned that his response had to be extreme. "You've just messed around with a big boy," he said. "Now get outside. I'm going to kill you."

In those days, Taylor often carried a range of knives, tucked around his waistband. He walked out into the night air and waited, his favourite nine-inch in his grip. Eventually he heard the door open behind him. He spun around and planted the blade square in the man's chest then pulled it smartly out. It made a sound as the air rushed into the wound. Squick. He swung it again, aiming at the man's temple, but missed. The injuries wouldn't prove mortal but it was time to leave. And at that point, in Taylor's words, he went "on the rampage".

Conscious that two attempted murders could lead to a hefty sentence, he wanted to settle old scores while he still could. As the attacks mounted up over the subsequent days, he began to get phone calls saying that police were blocking off whole sections of Peterlee and raiding houses looking for him. He had been on the run before, but never like this.

One night, he was sleeping in a car with some friends. He awoke with a start. There were voices, and torches were shining in through the steamed-up windows. Cops. Taylor sat in silence, put his hand on the ignition key and contemplated his next move.

Seven years earlier, the police had been closing in on another high-value target. His name was Michael Emmett and he was an international drug smuggler. Charismatic, quick-witted, a commanding voice straight out of a Mike Hodges film, he was of a breed of London gangster that today has almost died. His father, Brian, used to run with the Krays, and Emmett was widely respected for his careful, business-like approach to crime.

Following a stretch in prison, he was approached by an underworld connection who asked him for help getting some narcotics into Britain. One of Emmett's associates duly enlisted a fisherman in Bideford, Devon, who agreed to meet a mother ship 200 miles off the coast of Land's End and pick up four metric tonnes of Indian cannabis resin, worth about £13 million. It was to be the largest ever known importation of cannabis to the UK. "The people we were working with were massive," Emmett, now 55, recalls. "Everything was done in code, no phones, different names."

On 7 November 1993, the fisherman made his trip. He had spent the previous three weeks stockpiling 96 boxes of cod, among which to secrete the drugs. The rendezvous went as planned and the contraband arrived on English shores to be loaded on to a fishmonger's van. Emmett was stationed at a nearby farmhouse with two others, to make sure there were no hitches.

Just before midnight, they phoned the van driver, but the line went dead. Emmett was worried, so the three drove out to the quayside. Suddenly a car came haring towards them on their side of the road. As it got closer, massive halogen lights switched on in front of them. A voice came over a loudhailer: "Michael Emmett, get out of the car. Put your hands above your head." Emmett was not minded to do so, but the driver, an old bank robber, had frozen at the wheel. Emmett put his finger on the door lock so he couldn't run. "Go - go!" Emmett shouted. "They're going to kill us, Michael," the driver replied, reluctantly pressing on the accelerator.

The car only got 20 metres further. The police - around 12 armed officers and 60 regulars - were everywhere. They dragged his other accomplice out of the back seat. Emmett opened the door and stepped out. "Get on the floor!" screamed the policemen.

Emmett remained standing, trying to process what was happening. He wanted life to stop there and then. He wanted it to go back to Saturday, he wanted it to be the day before. A blow to his kidneys knocked him to his knees and the cuffs came on. The chief officer, who had been attempting to bust Emmett for 18 months, came running over. "We f***ing got you," he said. "A penny for your thoughts?"

Emmett looked up at the sky. It was a very windy night and the clouds were being blown everywhere. He turned to the policeman. "My three children," he said, imagining the time he'd likely spend behind bars. "My kids. Now f*** off and leave me alone."

He was sentenced to 12-and-a-half years. His father had also been arrested for being involved in the cannabis plot and they would serve time together. The first portion of their sentence was at HMP Exeter. There, Emmett befriended the chaplain, mainly so he could use the phone to call his then girlfriend, Daniella. To curry favour, Emmett went to chapel on Sundays. He even joined in with a prayer group.

One day, in the autumn of 1994, he was reading a copy of the Mail On Sunday and saw a picture of Holy Trinity Brompton (HTB), the church in Kensington, west London, that Daniella had started attending with her friend, the page-three girl Samantha Fox. The photo showed queues of people outside, hundreds of them. He went down to show the chaplain. "Oh, that's Alpha," the chaplain explained. "That's what we want to get in the prison."

We used to be a bit embarrassed about the Holy Spirit because it sounded weird. Now we live in a world that's much more open (Nicky Gumbel)

Alpha was created at HTB in 1977 as a refresher course in Christianity for lacklustre churchgoers. It was small-scale, and its members were elderly. Thirteen years later, Nicky Gumbel, a Cambridge-educated priest, took charge of Alpha and it transformed.

Most importantly, it was re-nosed to appeal particularly to agnostics. Gumbel erased the Bible-study aspect (if you don't believe in the Bible, what good is that?), and the introductory talk on "How can I be sure of my faith?" went the same way. He made its 15 sessions livelier, with guest speakers and music, and he was at pains to ensure it never felt preachy. Greater attention was paid to marketing: it downplayed references to religion, talking instead about "the meaning of life". His instincts were vindicated - and then some. HTB started converting hardened nonbelievers into committed Christians by their thousands.

Gumbel is now the vicar at HTB and still running Alpha today, though it has spread far beyond SW7. The course operates in 169 countries at more than 66,000 locations (mostly churches, ranging from Catholic to Evangelical - HTB falls into the latter category). In a post-Dawkins era, despite the increasing demonisation of Christians, the average age at HTB is 27. Bear Grylls, Jonathan Aitken, Geri Halliwell and the Archbishop of Canterbury are all Alpha alumni, as are 24 million others.

Its crucial feature is an emphasis on the Holy Spirit, which is explored on a weekend away that typically falls between session seven and eight, when guests are encouraged to speak in tongues. In short, they have religious experiences. "I think that's why it works," says Gumbel. "We used to be a bit embarrassed about the Holy Spirit because it sounded weird. Now we live in a world that's much more open: the part young people find hard is the Bible and authority, but if they can have an experience of God that's fantastic."

Alpha's prominence has attracted some negative press. "But even that's changed. The media is not as critical as it used to be," says Gumbel. "When people come and see it, they don't find too much to criticise. They say it's upper middle class until they realise it's not; they say it's forced down your throat, until they go to one of the small discussion groups and find quite the opposite."

Back in 1994, Alpha might have been in the public eye but it certainly wasn't in the prison system. Exeter prison's chaplain was excited about its potential, though, because of recent stories about congregations being spontaneously overcome by the Holy Spirit, rolling on the floor, weeping and wailing. If it was that effective, perhaps it could convert more troubled inmates? Emmett suggested they invite Gumbel to come down to the prison. Instead, Gumbel sent a team to hold a service.

And so it was that one autumn day, a chapel full of criminals who had largely been cajoled along by Emmett and his father, found themselves stomping their feet and singing about Jesus. But the most surprising moment was yet to come. One of the Kensington cohort said a prayer, "Come, Holy Spirit." Right then, Emmett's father fell over. "And before I managed to get to him," Emmett recounts, "I had this overwhelming sense that God is real, a feeling of an introduction, and it really filled me up. I can remember the words coming out my mouth, 'It doesn't have to be like this no more.' People started to cry; people started to laugh. My dad was on his back. He's never been the happiest of souls, and he was laughing and laughing. And then as quickly as it started - it had been going on for about 15 minutes - the prison officer said, 'That's it boys, bang up!'"

After Exeter, Emmett was transferred to three further prisons: Swaleside, Maidstone and Blantyre. He brought Alpha to all of them and, because he had clout, the sessions were well attended. Others, in turn, took it with them when they were transferred, and it spread stealthily throughout the system, becoming - by accident - an important rehabilitation tool. Once Emmett was released, he volunteered to help export it to further jails in Hong Kong, South Africa, and South Korea. Today, 250,000 inmates worldwide have completed Alpha; in Britain, it is offered in 80 per cent of prisons. Those who take it, and also sign up for the help of its sister charity Caring For Ex-Offenders (CFEO) - which meets ex-cons at the prison gate, links them with a church and mentors them closely - have a reoffending rate of just 17 per cent, compared to the national average of 58 per cent for those serving less than 12 months. "God could not have chosen a better messenger," says Gumbel, of Emmett. "St Paul was a bright guy, which was what was needed in the Roman world, and in the prison world Michael was the classic guy to choose."

Shane Taylor was sitting in his cell at HMP Holme House near Middlesborough, and he was angry. Angry that he hadn't mustered the energy to escape when the police found him in the car that night (he was now consequently halfway through a sentence of four years and nine months for GBH with intent) and angry that a prison officer had deliberately, he suspected, not unlocked him for gym that day. He decided to take revenge.

Just after "association time", in which prisoners are allowed to mix with each other, Taylor told a friend to start lobbing balls from the pool table at the officer who had crossed him, just as a distraction - he'd do the rest. His friend was keen to earn Taylor's respect and did as he was told. Soon, the officer was ducking and diving but couldn't escape: 60 other prisoners had blocked the exits.

The officer drew his stave and came running at Taylor, who was clearly orchestrating the trouble. Taylor reached for the glass coffee jar behind him, smashed it and picked up a shard. He jabbed and slashed at the officer, cutting the man's hands as he tried to protect himself and then stabbing him in the legs. Eventually, other officers arrived and piled on top of Taylor. "I had done what I needed to do," recalls Taylor, "so I just went down." He was put in segregation.

A week-and-a-half later, there was a riot at Holme House. The authorities said it was provoked by Taylor's actions. He had a further four years added to his sentence, and was treated from then on as a Category A prisoner. He spent most of his days in segregation. For months at a time, his food would be delivered through a secure hatch in his door, and he would be escorted to the showers by officers in full riot gear. He was put on the "ghost train", as inmates call it, getting moved from maximum security jail to maximum security jail. Whenever he was put back on a wing, he would inevitably start trouble. His standard tactic was to retreat to his cell after a fight, strip naked so he was less easy to restrain, and wait to do battle with the officers. The Home Office came to know him as one of the six most dangerous prisoners in the country.

It's Wednesday afternoon at a major London prison, and the introductory session for its first Alpha course of 2014 is about to start. The prison itself - which GQ has agreed not to name - is Victorian; a recent report criticised its overcrowded conditions and vermin infestations. Yet here in the chapel it is spacious and clean. The walls at the front are painted pink. The stained-glass windows are covered in attractive lattice work, not immediately recognisable as bars.

Reverend Paul Cowley, who runs CFEO, is there volunteering; so too is Emmy Wilson, who led Emmett's transformative service at Exeter, all those years ago. More than 50 inmates have indicated an interest in coming to today's session, which is a high number. "Perhaps they thought they were signing up for an engineering class or something," the chaplain wonders.

At two o'clock, they start to trickle in. Far fewer turn up than expected - ten in all. It seems that nobody from C or J wings is present. They haven't been unlocked, denying those inmates their start on the road to a better life. It's not clear why this has happened. A prison insider will later suggest that perhaps an officer was distracted or simply couldn't be bothered.

Just like on the outside, the Alpha sessions in prison comprise food, a speech and a discussion

Just like on the outside, the Alpha sessions in prison comprise food, a speech and a discussion. The chaplain introduces Cowley to the lectern. He talks about growing up with parents who were functioning alcoholics. He started burgling houses, but "was really pathetic at it, so kept getting caught". Now, having found faith through Alpha, he says, he is married, ordained and has a job he loves.

There's a ten-minute coffee period, before the inmates break out into three small groups. They talk about why they're here. Unlike regular Alpha, where it can take a few weeks for barriers to come down, they open up instantly. There's no pretence - they've already been caught. "I had a phone call yesterday saying my brother had died," says one, on the verge of tears. "Obviously that was a bit of a slap in the face. It's made me start thinking about the afterlife, and what happens after you die."

But before the groups can continue, officers suddenly appear at the back of the chapel. Something's wrong. The chaplain makes an announcement: "Please listen up, some people are going to be joining us now and we need to move all the furniture back as quickly as possible." It transpires that two prisoners had a fight in their cell, and one tried to burn it down. D wing is being evacuated, and the only space big enough to house the inmates is the chapel. The jail is on lockdown. Within minutes, all 110 seats are full. Row upon row of prisoners, looking up at the steel cross shining on the front wall. "If only they had come earlier," says Cowley. "We could have got them to join Alpha!"

Privately, Alpha sources fume about prisoners not being unlocked - this threatens its ability to rehabilitate inmates that are eager to change. But Chris Grayling, the justice secretary, insists that it is an occasional issue rather than an endemic problem. "What you're describing is not commonplace," Grayling told GQ recently, sitting in his office at the Ministry of Justice. "There are always operational reasons why things don't go according to plan."

Until recently, the government hasn't offered ongoing support for Alpha and CFEO's work. Given that - regardless of one's beliefs - faith-based programmes produce such strong results, why has this taken so long to change? "I don't really know," says Grayling. "But it's time it did."

Indeed, Grayling's 2015 probation reforms have a £450m budget to involve more charity organisations in rehabilitation. "They'll be paid a significant proportion of their fee for just doing the job, but some of it they'll have to earn for bringing down reoffending." Clearly, CFEO stands to benefit. "I want the mentoring skills that exist in the voluntary sector, very often from former offenders who themselves have gone straight. Few people leave prison with a determination to reoffend, but they get lost."

Still, amid budget cuts, ten UK prisons allegedly no longer have the staff to provide Alpha at all. Grayling argues that a new procedure coming in "within the next couple of months" will see less locking up in the middle of the day, freeing up time for prisoners to be supervised outside of their cells. So those ten prisons will get their Alpha courses back? "We don't tell every governor how to run their own prison," he says. "But I'm not aware of any practical reason why the chaplaincy and volunteers outside shouldn't be able to come in and run the Alpha course."

On an overcast January day in Middlesborough town centre, Shane Taylor, now aged 33, is sitting with GQ in an all-you-can-eat Chinese buffet. Earlier, he bought a new colouring book for his children, Isaac, Grace and Angel. In a couple of weeks, his wife will give birth to his fourth, Jacob. He did his Alpha course in 2005, while at HMP Long Lartin, one of 45,000 British inmates to have done so since Michael Emmett brought it into the system. And, for Taylor, it happened by mistake.

One day an officer opened his door and said he had to go to an educational class. When he arrived he was told he wasn't on the list, and directed to the chapel. It was midway through Alpha. He sat at the back for a moment and was considering leaving when a fellow inmate told him to stay for the free coffee and biscuits. Tempted, Taylor signed up immediately.

Its message of forgiveness came to attract him. "I had always thought there were good and bad people," he says. "I thought I was bad, so I was going to hell no matter what I did." A few weeks later, the course had reached its Holy Spirit session. Taylor was hoping to feel something, but he didn't. He was disappointed. The chaplain asked him to come down to his office later. "I went back as he'd asked and he prayed for me in tongues. I remember feeling daft, but he asked me to pray as well. And I just said, 'God, if you're real, come into my life, because I hate the way I am.' Then the chaplain and I started talking and I started feeling an energy in my stomach. This feeling rose up and I stopped talking. I started to feel my eyes bubble up, and just sobbed and sobbed. I knew God was real then."

As ferociously as he had thrown himself into violent crime, he became a zealous Christian. The officers were, obviously, incredulous. He lost friends, too. "People would mock me and I wouldn't care." Unwavering, he helped out on two further Alphas. The officers began to accept they had been proved wrong.

That's not to say there weren't relapses. "I had an incident with an inmate where he pulled a knife on me and I just flipped and tried to grab him into my cell," he recalls. "After, I shut the door and fell to my knees and started crying. I thought, 'I'm still the same person.'" The chaplain reassured him that simply being penitent meant he had changed. Things take time.

Taylor is about to start working for Paul Cowley at CFEO, promoting the charity in the northeast. He's repentant for his crimes, which, if pressed, he puts down to a combination of mental illness and a chaotic childhood ("There's no excuse for what I've done, though. I wish I had never done it"), and has been out for seven years without reoffending.

It's impossible to imagine where he'd be now, if he hadn't ended up in the chapel that day. "I'll tell you what was on my mind before I became a Christian, what I was planning to do after I got released. There were two prison officers that I was going to find. I was going to tie these officers up, brutalise them a bit, and kill their families in front of them. I was going to say to them, 'Look what you've done.' And then kill them, too." If he had got life, he wouldn't have cared, because he'd have won - that's just how he used to think. "Don't ask me why," he says. "Maybe it was the devil."

alpha.org

Originally published in the June 2014 issue of British GQ.