The white envelope that arrived at the family home would have been innocuous enough, were it not for the emblem in the top left corner. For the married father-of-two to whom it was addressed the words Polismyndigheten i Stockholms län - Stockholm County police - were the first clue that his visit to a prostitute had not been as discreet as he might have imagined.
The 52-year-old is one of more than 500 men convicted in Sweden under legislation introduced in 1999 criminalising the purchase or attempted purchase of sex, and decriminalising its sale, with the aim of reducing levels of prostitution and trafficking in women by cutting demand. The country views prostitution as a male violence against women and children, officially acknowledging it as a form of exploitation that is a barrier to gender equality. The Swedish term for a man who buys sex is torsk, meaning cod.
Many of those apprehended have families and well-paid jobs, authorities say. Four judges are among those convicted.
Although the options include a jail term of up to six months, all the men so far have received fines, which are based on earnings and whether the buyer has offended before. The largest penalty handed out was to a company director on a yearly salary of 1,440,000 kronor, who paid 70,000 kronor (£5,600). Three months later he was caught again. Supporters and critics agree street prostitution has been reduced. Agneta Borg, who has run Stockholm's social services project working with prostitutes for 11 years, estimates street prostitution is now 55% or 60% of what it was.
Government figures estimated there were around 2,500 native Swedes or permanent residents from abroad working as prostitutes in 1998, and only 1,500 in 2003. But the sale of sex off the streets, in brothels, strip clubs, massage parlours and hotel bars, remains largely unquantifiable, and it has soared online. It is there, according to police, that many trafficked women can be found.
The number of women trafficked to Sweden has risen, with those from Estonia, Russia, Poland and Lithuania most prominent. In 2003 it was estimated at 400-600; Kajsa Wahlberg, a detective inspector who is the country's national rapporteur on human trafficking, believes it could be around 1,000 today.
But trafficking has risen everywhere, she says, and the Swedish figure is nothing compared with its Scandinavian neighbours. Wahlberg estimates the figure in Norway and Denmark is around 6,000, and between 12,000 and 15,000 in Finland. All three countries have about half the population of Sweden.
Criminalising customers makes it harder for trafficking operations to operate, she says. "They have to be very discreet. They can only run two or three women at a time, and they have to keep moving around because neighbours complain to us." She rejects claims the law puts prostitutes at greater risk of violence by driving the sex industry underground.
"The biggest part of prostitution has always taken place indoors and underground. We don't get reports saying women in prostitution are being more violated than before. There are always risks of violence in prostitution." Most of the prosecuted men are caught during surveillance on suspected brothels because their evidence can be used to convict the pimps and traffickers.
In the last two years 77 trafficked women have been taken out of sex work in the Stockholm area after police operations. In many cases the man's wife or partner gets to the police-embossed envelope before he does and opens it to find a letter telling the recipient he is wanted for questioning, or is being fined. "We get telephone calls from men and women telling us we're destroying their marriage," says Ann Martin of the interrogation team in Stockholm. "The wives are terrified, frustrated and angry. They ask what this is about. We tell them to talk to their husbands."
On Malmskillnadgatan, the single street that forms Stockholm's traditional red light district, the complaint is that the law has made conditions tough.
Wahlberg says one might have seen around 40 prostitutes there 10 years ago: now only a few congregate. During one evening just 12 bundle themselves up against the cold to ply their trade, apparently with limited success.
One is politely rebuffed by a grey-haired man who passes through innocently wearing a festive red and white bobble hat. "He doesn't want to be my Santa Claus!" she says. Having settled in Sweden after coming from Venezuela in the early 90s and worked as a cleaner and a waitress she turned to prostitution two years ago. She is now 31. "It's difficult to find a job here and I need the money. There's a lot of competition now, and the customers are afraid," she said.
"My friend who worked here before the law changed said you could make 20,000 kronor in a night; now it is much lower than that. Everyone has goals. I would like to buy my own house in Sweden and get a normal job, some education, a profession."
An older woman fumbling for a lighter says she is fed up with everyone assuming her work is "tragic and miserable. It's like anything: some days it's OK and some days it stinks."
Sven-Axel Månsson, of the University of Malmo, says that for occasional sex buyers who get caught and prosecuted the shame can put them off, but for the habitual user it is less likely to act as a deterrent. Such men use internet forums to complain bitterly about Sweden's law. Some travel to Copenhagen, to avoid the risks of using prostitutes in their home country, Månsson says.
In Malmskillnadgatan the same handful of vehicles circle the block endlessly. Other men approach the shivering women on foot: some eye the scene from a distance. Marked police cars drive through slowly a couple of times, without stopping.
By 1.30am the street is almost still. Two men approach in a car and draw to a halt. One gets out: his eyes are bloodshot, his mouth droops and he is missing some bottom teeth. He speaks in Swedish and then English: "I am looking to meet some nice girls."
Once he realises he is not talking to a prostitute, he insists his motives are innocent. But he goes on: "If I have a woman at home she has to be very strong to feed me, because I love sex. She will be tired from working and she will not be able to feed me."