Along with John Grisham, he is the most widely read author among British prisoners, but what makes Stephen Leather a hit among guest of Her Majesty? Nick Morrison reports.

WE'RE in the lounge of the Vermont Hotel in Newcastle, elegant and discreet at the city end of the High Level Bridge, and it's about half an hour into the interview when Stephen Leather reaches into his holdall and pulls out a small, black device, about the size and shape of a mobile phone, except with no keypad and with two aerial-like horns sticking out of one end. After fiddling with it for a couple of seconds, and without interrupting his flow, he puts it away and carries on.

Another half-hour, the interview over and I'm just taking my leave, when he brings the device out again, this time holding it up for inspection. It's a mobile phone blocker, he says, before deciding that further explanation is necessary.

"That woman over there" - gesturing at the now-empty other side of the room - "was really annoying me, so I used this. It switches the signal off for mobile phones within about 30 yards. She was annoying me by talking on the phone, so I just switched her off. I don't think it's illegal." Clearly, working on the seedier side of life has its advantages.

Leather was a journalist before he turned author, so far turning out 15 novels, starting with IRA thrillers before moving into other areas of crime when the Good Friday Agreement killed his original genre. His latest, Hard Landing, is set largely in a prison, with an undercover policeman sent in to get close to a drug dealer who's carried on running his business from the inside.

His watchword is authenticity, which is why he's fresh from spending the morning in Durham Prison, one of ten jails he's visiting as part of a book-reading tour. It's a chance for the inmates to meet one of their favourite writers - he's one of the most borrowed authors in prison libraries, second only to John Grisham - and a chance for him to gauge whether his research has paid off. After talking about how he became a writer and readings from his latest novel, he asks for questions, and it's then he finds out if he's on the right track.

"It went really well and they were all saying I had captured what life is like in a prison, and they're not shy about coming forward," he says. "Normally if you give a reading and say 'Are there any questions?', there are no questions, but in prison there are always lots of questions, about where my ideas come from, who my villains are based on, if anyone's ever come looking for me because of what I've written about them, what sort of guns I've fired.

"The first time it was daunting, but as it has gone on I've got more and more confident. I'm talking to fans and I get as much out of it as they do - I get feedback on the new book and I get to meet the sort of guys I'm writing about.

"If you go into prison and meet 25 guys, you are not looking at 25 offences, they're regular guys. They're not monsters. They're just guys who have made a bad decision and gone down the wrong path. There are monsters in prison, but they're not the guys that come to see me."

Leather has also written for TV, shows including London's Burning and The Knock, and it was working on the latter which saw his interest in crime turn into a career. Meeting drugs squad officers and Customs officers as part of his research brought him into contact with another side of life, as well as with people who would prove to be important sources for many of his stories. Writing for The Knock also gives him kudos with some prisoners, who count the show among their favourites and respond by telling him their own stories, which in turn provides him with more material.

"You are writing about the world they know and characters they know, but it is fiction. If I want to write about drug dealers, I talk to drug dealers. If it's a book about prostitution, I speak to vice squad officers and working girls and escort agencies. The latest book is about prisons, so I went to prisons to do research and spoke to Customs about the problems of powerful drug dealers behind bars.

"I meet guys on both sides of the law and they're just regular guys. A guy might be moving huge hauls of drugs around the world, but he probably goes to PTA meetings. Villains aren't villains all the time. In prison, they love to see villains as real people, and in my books you have villains but you see them as fully rounded characters. I don't just have a bad guy doing things, I have him being nice to his wife and kids."

Leather takes his quest for authenticity seriously, even down to learning how to fire and strip a gun. Again, his friends come in handy. "I know a guy who was in the SAS and he runs training courses in Slovenia, where you get to fire automatic weapons and a whole load of handguns to your heart's content," he says.

"I've been to Cambodia a few times - you can fire really heavy stuff there, RPGs (Rocket Propelled Grenades), mortars, grenades. You have to tell them what you want a day in advance so they can go and steal it from the army barracks. You can even buy a water buffalo to shoot at for around $200 but I never did that.

'IT is fun enough that I would do it whether or not I was writing books, but one time I had a hand grenade, pulled the pin and threw it and then I was standing thinking it would be nice to see what it was like when it explodes. This Cambodian guy grabbed me and threw me to the ground and we were covered in debris."

It's through this level of research that he knows an Uzi pulls up and to the right when you fire it, as well as that the bristles come off a prison issue toothbrush the first time you use it. All this helps to convince some of his most important readers that he knows what he's talking about.

But his desire to find out how things really happen has landed him in trouble on more than one occasion, particularly in Dublin, where he now spends much of his time.

"I hang around a lot of nightclubs and I was talking to one guy who said he was doing a lot of business in Miami and I asked what kind of visa did he have, so he threw me up against the wall and put his hand around my throat. Another time a guy sat me down and wanted to know what I was doing.

"If I were a journalist it would be different, but once they know I write fiction they start telling me stuff and they relax around me. I become their tame writer." But even if it has occasionally led him into trouble, his walk on the wild side has also given him an insight into a world few of us encounter in any depth, and the result is perhaps a surprising view of those on the wrong side of the law.

"I think I like low lifes. Low lifes are fun, they are fun people," he says. "The bad guys I know have far better cars and go out with far prettier girls than the good guys."

* Hard Landing, by Stephen Leather, is published by Hodder and Stoughton (£10.99).