I meet Angela not half a mile from where she works in Soho. Later this evening, she will change out of her girl-next-door outfit and put on a very short skirt and small bikini top. She will strap on six-inch heels over fishnet stockings and apply a thick layer of scarlet blusher. Then she will stand in the freezing cold outside a spangly curtained doorway and try to entice men into one of London's notorious "clip joints".

With the help of a burly "security man", Angela explains calmly over morning cappuccino, she and her colleagues will then rob these men of anything up to £3,000 each. Angela, the 24-year-old "hostess" or " doorgirl", will "entertain" four or five "customers" per night, and earn from £800 to £1,000 this week for her part in a simple, brutal and highly illegal racket. Despite the money, Angela has promised herself that she will give up her criminal career by the end of the year and get out of Soho before she becomes "unable to look at myself in the mirror".

For this reason she has decided to talk to the Evening Standard - the first clip-joint girl to break cover and describe the scam from the inside. An article in the paper earlier this year exposing the "clubs" caused a brief but dramatic downturn in business, she says. "I've been thinking about leaving for a long time. I don't care much about most of the men we rip off, but I do know that what we're doing is wrong."

Up to 20 such illegal sex clubs exist in London's most intractably seedy quarter, a triangle to the south of Soho including Great Windmill, Rupert and Brewer streets. In recent years the police have had some success in reducing crime in the area and closing unlicensed premises. But the lucrative clip joints still flourish. As Angela coolly explains, and as the police confirm, unless the male victims of this type of vicious extortion come forward and report the crime, there is little anyone can do to stamp it out.

Angela claims that she "fell into" the sex industry, and the clip-joint business, almost five years ago when she first came to London - perfectly legally, she says - from her native Poland.

She arrived with dreams of starting her own business, like her parents who own a couple of grocery stores. First she had to learn English - it is now excellent, spattered with a colourful Soho vernacular - and after that, she enrolled on a business degree course at London Metropolitan University. With fees for non-British students and living expenses of £12,000 a year, Angela quickly realised she could not live on waitressing alone. So she and a Polish friend answered an advert in an expatriate news-sheet promising profitable rewards for attractive young women prepared to "look after" men in Soho clubs.

Until she turned up for the " interview" and saw "the pictures of naked women" that decorated the walls of the bar, Angela, then just 18, says she assumed that "looking after" meant "talking to lonely men and keeping them company".

Now she has her business degree, why does she stay? "Why do any of the girls in Soho stay?" she replies. "Some have been there 10, 15, 20 years. It's the money, of course. Some of the girls are from good English homes, from lovely families. They even live at home and tell their parents they are going out for the night with friends, and then come to work in Soho.

I don't know how their mothers do not see the make-up they wear or the little dresses ... But can they earn £1,000 a week as a junior office assistant-In a shoe shop? Of course not. She also admits that many of the girls who work the clip joints are addicted to hard drugs - heroin, crack and cocaine - and are trapped in this way of life by their habit.

The clip-joint racket - Angela prefers the term "rip-off" - combines the often unfulfilled promise of sex with simple blackmail and the threat of extreme violence. The crime is all the more remarkable for its exploitation of extraordinary male naivety, and its relatively sophisticated use of various " subcontracted" services around Soho.

The con trick begins when girls like Angela attract a "customer" into the premises by offering a striptease or a massage for as little as £5. "Are they dumb?" she asks, laughing. You're not going to get anything for that price. She then leads him downstairs to a dingy bar, often furnished with no more than two or three tables, and offers him a drink.

It is at this point that the man begins to discover what he has got himself into. Of course, the "striptease" costs substantially more than £5. The girls, says Angela, are highly adept at judging a man's income and vulnerability to blackmail from his appearance, and are allowed to deviate from an unofficial price list according to their own assessment. "It's people-management," says Angela gleefully.

A striptease might, in fact, cost between £100 and £600, depending on the cards in a man's wallet, the existence of a wedding ring on his finger or in his pocket (the security men will search a customer if he refuses to pay) or his nationality. We call Americans ' piggy-banks', but the Japanese and the Malaysian men are the very best because they always carry so much cash.

The doorgirls talk to their customers for a while, perhaps half an hour, and explain the costs while the man drinks. Half the men are British and half are foreign, mostly tourists and businessmen, says Angela. You make conversation, ask them what they are doing in London. He might say he is here on holiday. Perhaps he has left his wife and children shopping at the Trocadero mall and wandered off to see the sights. We have 'cocktails' of orange juice and Ribena while they drink champagne or beer. They think we're drinking alcohol with them, but, of course, if we did that, we would get drunk very quickly."

What the men do not know at this point is that each glass will cost precisely £250. That's the standard price across most of the clubs. We tell them they're paying for my company, to sit with me and talk to me. He has one drink and no show, he pays £250. He has two drinks, it's £500. He has two drinks and a show, he might pay £800 or £1,000. The most I have seen a man pay for two hours in the club is £3,000.

The floor shows are performed by strippers who "freelance" from club to club. In a single night these girls will often walk around Soho for several hours, says Angela, visiting the clubs in turn at the request of the "hostesses" or doorgirls and pocketing a meagre £30-£50 for each performance.

Angela knows them all, but claims that she herself does not strip. If a man wants sex, then the clip joints lease the services of yet another freelance performer. The security man will take the customer to a prostitute in a nearby flat - they have unwritten contracts with a number of women in the area - where the woman receives another £30 to £50 and the clip joint takes the bulk of the fee. Of course, the men have to pay first. If they don't like the look of the woman, they still have no option but to pay.

Most customers do not have enough money in their wallets to pay up front, so the security men - most are Eastern European or Maltese - march them to a cash point and wait while they extract the fee. Those that refuse are threatened with a severe beating. Whether or not they carry out that threat depends on the club, Some don't want the aggro and prefer the straight blackmail route. Most customers will have something to lose just by entering a place like that.

We have cameras and we tell them they are on film. We look for the weakest point in a man, usually the fact that he is married. A lot of men are so stupid they think it's their fault they have got into the mess, and it's just easier to pay up. Sometimes I feel sorry for them It is pathetic to watch them when they see their bill. I have seen men down on their knees begging a hostess to let them go, saying that their wives will find out if they take that much money out of their account.

She pauses and smiles at me. I'm not that bad, I try to be kind. If a man comes in and it is clear that he cannot afford it, I tell him to go immediately, before anyone sees him.

But, yes, there is a lot of violence, too. Customers who "get heavy" with the girls are often beaten up, says Angela - who goes on to describe an extraordinary incident in which a man was so badly beaten, she claims he later died in hospital. The police say they have no knowledge of this, but Angela maintains that the murder could never have been proved and that the men responsible are still at work in Soho.

Whether or not she is telling the truth, the fact remains that many "customers", particularly those who attempt to pick a fight themselves in response to demands for money, are violently "mugged" for their cash. It's incidents like these that have convinced Angela to leave Soho. This is not how I was brought up, or what my parents would like me to do. They would be horrified if they knew. The men we rip off may be very stupid indeed. But I am not.