THE Balmoral occupies a pretty unique place in Elliot Castro's heart. As a young boy, he stood outside, dreaming of one day living among the hotel's rich and successful clientele. Years later, he was arrested at the front desk for trying to pay for a room with a stolen card. Later still, he brought his mother here for dinner during his biggest spending spree as one of Britain's most successful credit card fraudsters, spending £42,000 in four days. How does it feel to be back? "It's a little bit unusual," he says, looking around the presidential suite with a sheepish smile.

Castro's used to places like this. For four years, the young working class Glaswegian mastered looking like he belonged in the world's most expensive hotels, rubbing shoulders with Bono and gambling thousands of pounds of other people's money in the casinos of Monte Carlo. Travelling first class from Europe and Canada to South America and the Caribbean, he bought champagne and designer gear with the fervour of a man who knew one day it would all come crashing down. How much did he get through before getting caught? "I wasn't exactly keeping records," he laughs. "But I'd pretty confidently say seven figures."

Today, he doesn't look like he belongs, dressed in jeans, trainers and a tracksuit top, as if to highlight the fact he's left that life behind. In person, he's surprisingly down to earth, funny and friendly. And although it could all be an act (I wouldn't be the first to be taken in), he seems genuine. He's clearly had the time of his life travelling the world, but he's cautious when answering questions not to appear boastful or lacking in remorse.

The biggest question of all, of course, is how did all this happen? "I could talk all day about where it all started," he says. "The truth is, I don't think I'll ever know." Elliot Castro had a rootless childhood. Born in Aberdeen, his family were poor and moved to Chile, where Castro's father had family. Their attempt at a new life was unsuccessful, though, and they moved back to Scotland, settling in Battlefield in Glasgow. "Moving about was turbulent," he recalls. "It made it difficult to create lasting relationships. I was pretty lonely as a kid."

At school he was a misfit, physically bullied and often isolated from the other children. With a photographic memory and an appetite for learning, he excelled initially but became bored and disruptive, constantly seeking attention. "I was a difficult child, for teachers and pupils. I could never understand the way other pupils carried on with each other, the things they'd laugh at. I've always felt different." So different and difficult, in fact, that he was expelled from four schools and spent time in Yorkhill Hospital's department of child and family psychiatry and the experimental Keppenburn Unit in Largs.

Anyone looking for Castro's hallelujah' moment might look to the day he convinced his young classmates he was a wizard. "That was my defining moment of realisation of what you can do with words," he says. A psychological evaluation for a later criminal hearing said of Castro: "He has very low self-confidence and poor social skills. He attempts to overcome this by pretending he is somebody he is not." The wizard never really went away.

While still at school he started forging train tickets, which he used to travel around Scotland. Crime, he says, even then, was a way of opening up a world that was otherwise beyond his reach. "I never had friends come knocking for me and asking if I wanted to go out, like other kids. I'd go out around the area or for a walk down to the river, but that was it. Those tickets were a kind of escape for me." Then, in his early teens, Castro found a credit card at a party and swiftly put it to use. "I got caught, that first time," he laughs. "But I was already intrigued - that you could go out and buy something with these little cards."

His crimes quickly escalated. He started stealing cards, watching for people to leave their coats or wallets unattended, using the money to buy haircuts, clothes, CDs There was an emotional buzz too. "Your heart beats faster. You've given over the card and the assistant's running it through the system, and there's that five seconds that it takes for the machine to come back, where you're thinking, Is it going to go through or am I going to hear that beep?' When it works, it's a thrill."

A call centre job introduced him to lists of people's personal credit information. "I've always had that thing - problem-solving, I suppose - where you can see how things connect. There was the realisation that if I had people's personal details, that would enable me to take over their account. That's the terminology the banks use, actually: account takeover'."

He found another way of getting people's personal details too: phoning hotels, he'd ask to be put through to a room, then pretend to be a hotel employee checking security information. He'd then phone the credit card company, using the person's passwords to order another card on their account, only this one would be sent to him.

Soon, his wallet was filled with cards, Castro dining out' on one until it was cancelled, then moving on to another. He even learned how to wire transfer money to himself. The scams were simple - it was the execution that was tricky. "I learned things like going into a shop and being able to know, in seconds, if there's something wrong. Or watching for little movements to suggest they were on to me - eye contact, people floating about a bit too close. Over the years, I developed a knowledge of bank procedures, too - what kind of security questions they ask and so on."

The biggest con was making the wealthy circles he was mixing in believe he was one of them. "I didn't grow up among those sort of people, so I had to learn very quickly how things were done. It's true that people with money do behave very differently. It's an attitude - the ease of everything. Actors talk about doing a lot of research to learn a part. But that was never a problem for me."

It didn't even matter that Castro was still barely 20. "People were surprised at how someone my age could afford to be living the way I was. I always looked a bit older than I was, which helped. But I had my story - that I worked for a hotel consultancy - and I stuck to it."

Ask Castro what the highlight of his four years was and he reels off a list. "One of my favourites was Niagara Falls, because it was so beautiful. The Caribbean was fantastic. My first time in London was pretty amazing" Everywhere he went there was champagne and cocktails, fine food, nightclubs, parties, sex. "Well, I wasn't celibate for four years - I'll put it like that."

In his four-day, £42,000 visit to Edinburgh, he spent £11,000 at Harvey Nichols, £5000 at The Opal Lounge, £7000 on a whim at Sotheby's and £12,000 on a Rolex Oyster President. "That was pretty fantastic. You buy something of that value, it's going to attract attention. So when everything went through, I was amazed. I couldn't wait to get somewhere where I could open the box and put it on my wrist."

The systems weren't flawless though. He was caught several times. "I've spent two and a half years of my life in prison. Four or five proper stretches and a couple of times where I was held overnight." How did he find prison life? "Young offenders was horrible. It's all wee boys - 18 to 21 - squaring up to each other." Worse, though, was The Don in Canada, where Castro spent two weeks in solitary confinement. "That was just a shit-hole," he says. "It wasn't just being alone for two weeks - it was dark as well. It's up there with the worst experiences of my life." There was the added shame of phoning home from prison too, his mother disappointed, his angry father refusing to come to the phone.

Wasn't all that a deterrent? "Evidently not," he jokes. "The first few times, I said to myself, When you get out, that's it. No more.' But it didn't happen. Instead, I spent a lot of time in prison thinking about my strategies and how to get better at what I was doing."

Out of prison, Castro moved from city to city, knowing the police and international fraud agencies, not to mention companies such as American Express and Expedia, were gradually catching up with him. It was also a lonely time, unable to visit his family for fear of being caught and with no friends to share his experiences with. To this end, he set up a base in Belfast, decking out a luxury bachelor pad.

"Belfast was one of the first places I stayed for any length of time. What interested me was creating friendships with people," he recalls. Out at bars and nightclubs seven days a week, Castro gradually developed a social circle. But like everything in his life, it was built on lies. "People asked where I got my money from. I couldn't exactly say, I'm a fraudster. I steal from banks.' Friendships weren't based on trust or truth, so no matter how much I liked a person or they liked me, there was always this niggling feeling."

Castro was stealing more money than he could spend, siphoning off thousands to a Swiss bank account. But a splurge at Harvey Nichols in Edinburgh was to be his last. "I was half way round the menswear department and I went to the bathroom. When I came out, there was a police officer stood in front of the door. A member of staff had just felt there was something wrong. I went over it a hundred times in my mind to try to work out exactly what it was she was suspicious about. I think maybe I was overly confident about the whole thing. It was just silly."

How did he feel when it was all over? "Initially, I was upset and angry at myself for being so stupid. But as time went on, it was like a ton of bricks being lifted off my shoulders."

Could he have been less greedy, more careful, and got away with it indefinitely? "No, the hound always catches the fox eventually. And it's hard not to be greedy when you've got so much money at your disposal."

In a world where money is everything and greed is good, perhaps people like Castro are always going to crop up. I wondered if he felt like the by-product of everything we see in magazines and on television. "Yes, I always liked films where there was luxury involved. Pretty Women was my favourite," he laughs, clearly embarrassed. "The nice hotel, lots of money. I saw those things and I wanted them." Where most people might spend their lives working legitimately towards becoming rich, Castro simply took what he wanted. "When I was younger, I didn't think my life was going anywhere. I didn't think there was any other way that I'd be able to do anything. That's the only explanation I can think of. I don't know anyone else who went to eight schools or spent time in a psychiatric ward. I felt pretty hopeless. So for me all this was an opportunity to go places I wanted to go."

It would be easy to make Castro the Mr Nice' of credit card fraud, a Catch Me If You Can-style rogue getting away with the adventure of a lifetime at the expense of major corporations. But it's important not to get too caught up in the romance.

Credit card fraud cost the UK £428 million last year, according to UK payments association APACS. Banks and companies spend millions on fighting fraud, costs that are passed on, through higher prices or service costs, to customers: us. In the wider picture, a recent report by the Association of Chief Police Officers (ACPO) suggested that the UK's annual loss to fraud is around £20 billion, which it equates to 200,000 police officers or a saving of £330 per person. The chip-and-pin system alone, brought in specifically to combat crimes like Castro's, cost the UK £1.1 billion. And though Castro is right when he says the victims of fraud have their money refunded by the banks, that doesn't account for the distress of identity theft or the inconvenience.

Does he have any idea how many people and organisations he stole from over the years? "It's very difficult to say, almost impossible to put a number on." Did he feel guilty about the fact his lifestyle was being paid for by other people? "I didn't really want to think about having an effect on people because I didn't want to feel bad about it. And at the time, I didn't personally think I was hurting anyone. Now, looking back, I can see what I did was wrong."

Strip away the audacious feats and many will see Castro simply as a common thief. How does he feel about that? "Everyone will have different thoughts. But I deeply apologise to anyone I affected. I'm genuinely sorry." He seems it, too. Even more so when talking about his parents' suffering. "My family didn't deserve to have journalists knocking at their door or police coming round to search the house. That still, to this day, tears me up."

In court, Castro got what the investigating detective Ralph Eastgate called the "right result" - two years in prison, out in one. And now he's out, he's determined to go straight. The deciding factor? Losing the friendships he'd started to form, which were arguably the reason he'd been stealing all along. "Before I went to Belfast, I didn't have anything to lose. Whereas once I'd met these people, I had friends - something I'd always wanted but never had. Getting caught was the end of that."

Twenty-four years old and back home in Battlefield, Castro has gradually convinced his parents that he's left his life of crime behind, after so many broken promises. "I think they're all right about it now," he says. "My mum says it's nice for me not to be gallivanting'. And things are a lot better with my dad."

Thinking back on his life as a super-criminal, Castro says, is "a bit mad", particularly the attention it has brought him. Film companies are interested in turning his story into a film. ("Who'd play Elliot?" I ask. "Daniel Radcliffe," suggests Neil Forsyth, co-author of Castro's book. "Why?" asks Castro, laughing. "Because he was a wizard?").

He claims not to have a penny left from his fraud activities and no secret stash. With his skills and knowledge, it must be tempting to return to his old tricks, but, he says, security systems will have moved on and he has no interest in cracking them all over again. Now working as a DJ in Glasgow, there's been a clear shift in his perspective. "It's different - I actually work for that money. It's not a great deal of cash, but it's enough to tide me over, and that's fine with me." Does he still crave the big money and the jet-setter lifestyle? "If I could do it properly, legitimately, I'd like to have money to pay rent every month and buy occasional nice things or a holiday. But I'm not interested in being obscenely wealthy."

It took him a pretty roundabout route, but he's arrived at the conclusion there are more important things than money. "Nowadays I have what I think are genuine friends. They know what I did in the past. It's so much nicer not having to lie to people."

Castro is penitent, but also honest enough to admit he'd be lying if he said he regretted everything. "I got to do a lot of things that people only dream of," he says, no doubt sifting through memories of cocktail parties in New York and boat trips in the Caribbean. "Some of that, I'll keep with me the rest of my life."

Other People's Money by Elliot Castro and Neil Forsyth is published by Pan MacMillan, £12.99