Jonathon Wheeler has lived in Bang Kwang prison for five and a half years. The story of how he got there is so familiar it has become a cliché. He was trapped in a gambling debt and threatened with death unless he carried a package out of Thailand to pay it off. The dealers tipped off customs and while Wheeler was stopped the people with serious quantities of heroin slipped through. Wheeler's life - working in a bar on the island of Ko Samui and kickboxing for a living - was over at the age of 33. He was sentenced to 50 years.

He could be home by now, but he has chosen to stay in a prison that is described as 'among the very worst in the world'. After four or eight years, depending on the length of the sentence, Thai authorities allow prisoners to transfer to a jail in their home country. U.S. and Australian prisoners are put on parole almost immediately. British law however, states that all prisoners must serve half their remaining sentence, which, given the draconian nature of sentences imposed in Thailand often means a great many years.

Sandra Gregory, a teacher from Yorkshire sentenced to 22 years in 1993, chose to take that route, returning to Britain after 4 years in Bang Kwang. Last weekend her family held a candlelit vigil outside Downing Street to mark the start of her eighth year of incarceration. But despite her parents' high profile campaign for her pardon, she is unlikely to be eligible for parole until December 2003.

Wheeler has declined to follow Gregory's example because he believes that despite the grim prison conditions he is better off in Bangkok, where at least there is some hope of early release. And he is not alone: Brian Mounsey, 41, could also be home by now, but has decided to stay and apply for a pardon or a reduction in sentence. There was great anticipation on the King's 72nd birthday in December, traditionally an excuse for an amnesty. In the event, all drug prisoners were excluded.

Jonathon Wheelers mother, Sheila Bucket, believes her son is making the right choice by staying put. She is only too aware that the prison is "disgusting, with rats and cats and cockroaches", but says that they have a "funny sort of freedom out there. They have a big yard, and they're outside for most of the day. A girl from England sent out money from her church, and so they have built a hut in the yard."

Wheeler could have come home 18 months ago " People who have done that tell him they wish they hadn't," says Bucket.

Gregory, 34, came home almost 3 years ago. Until recently, she was imprisoned in Durham prison, alongside Rosemary West. She is now in Cookham Wood, in Kent. "She's not in a good way," says her mother Doreen. The Gregory's describe Sandra's continued incarceration as a "huge waste of everybody's lives". Under British law, her crime would have merited a 4-year sentence. Doreen Gregory points to a recent case where a couple received sentences a third of the length of Sandra's for smuggling 30,000 timed the amount of heroin. The British government however is declining to write a letter to Thai authorities supporting their call for an appeal.

Sources within the foreign office suggest that a reform of the law, to bring it in line with that of the U.S or Australia, might be creeping on to the agenda. Officially, however, the idea is not entertained. The last thing the government wants is to be seen to be soft on drug offenders: prisoners and their relatives argue that they have been punished many times over and that they are no real danger to society.

For Paul, the question of transfer did not arise. Paul (not his real name) carried drugs out of Thailand, and was given a 100-year sentence. After four and a half years in Bang Kwang, he was pardoned on the grounds of terminal illness. Now, aged 29 and HIV-Positive, he has been home for 13 months. He looks well on a battery of drugs. "It's been hard, coming back" he says " I'm still not working or anything. You get used to being in an environment you know. My best mate was still there. I didn't want to leave him."

When he was sentenced, Paul had been living in Thailand for 5 years, but found his arrival in prison utterly bewildering. "I walked through the gates, and you don't know if you are coming or going. There's just people shouting at you. One guard with a glove on doing anal searches. He comes to me and I go, 'There's no way you're doing that.' I said OK you can do it, if that's the rule, if you change the glove. I'm not having that glove… Literally the fingers on it were brown."

Once Paul was diagnosed as HIV positive, he focused on his own survival. Around 10% of Bang Kwang inmates are infected. "If I had had the medicine I'm on now," he says, " there's a good chance that a guard would take half of it away and sell it on. Or someone's going to take a knife and stick it in my back to take it."

Conditions in Thai prisons, while bad for everybody, are made bearable if the prisoner has support from outside. "I didn't realise at first that you could buy fresh food," Paul recalls. "The first morning I thought how can I eat that? There's red rice, which is like brown rice but the lowest grade. And there's hairy fish-head soup. I took some and thought I was going to die."

"Five months after he got there Johnny trod on something and the cut became infected," his mother recalls. "I thought I was going to lose him. But if you can pay the money, you can always get to the hospitals. There's a really bad flu bug in the prison at the moment. TB is rife, and there's leprosy. They sit outside and scrape it off." The British embassy provides vitamins, and Prisoners Abroad also helps as much as it can.

Paul admits that he took heroin in prison. "You have to do something," he says. "I wish I hadn't. I felt better when I wasn't. But it's so tempting. I didn't share needles," he adds, "Until I knew I was HIV Positive."

It is chilling to realise that Paul, with his terminal illness is almost the lucky one. "The financial rewards will never be worth it," he says. "Never, It's really dumb, and I was really dumb. I knew what was going on, but there are hundreds of people in there who didn't. They've landed in the country, been given a suitcase, and they've taken it back out. They probably know what's in there, but if you're after the money you're going to convince yourself."

No Briton has ever survived the eight years that life prisoners must serve in Thailand before they can transfer. But Wheeler, Mounsey and others are trying to hold out.