A de luxe, call-girl ring? An international prostitution agency for the jet-set? Both descriptions are redolent of furs, jewels, penthouse suites and a kind of perverted glamour, but are hopelessly misleading. A trial which ended in Paris yesterday revealed something more disturbing: a casually arrogant conspiracy to purvey naive, star-struck young women to the rich and famous.

A failed fashion photographer, Jean-Pierre Bourgeois, 51, faces six years in jail for enticing, or tricking, 86 young women - some as young as 15 or 16 - into prostitution with the promise of a career in modelling or the movies. Three other people face lesser penalties when the court gives its reserved judgment next month.

Clients are said to have included the actor, Robert De Niro, the former tennis star, Wojtek Fibak, the French film producer, Alain Sarde, the former Emir of Qatar, one of the brothers of King Fahd of Saudi Arabia, and Christian Courtin, the head of Clarins, the large French cosmetics company.

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The case is not yet over. The other alleged, principal organiser of the conspiracy, Annika Brumark, 50, a one-time Swedish beauty queen, will be tried in May when her lawyer has recovered from a road accident. Two of the clients of the agency - Fibak and Sarde - are still under investigation and may yet face charges of rape and assault.

Brumark, it is alleged, was the real brains behind the network, taking 40 per cent of all the money paid by the clients. Bourgeois, at first, took no money. His reward was to force the glamour-befuddled girls to have sex with him. Gradually, he too was sucked into treating what began as a vicious game into a money-spinner.

Nadia M. was 20 years old when she fell into the silken trap extended by Bourgeois in 1996. A pathetically thin French girl of Moroccan origin, she told the court that she was a shop assistant, living in a welfare hostel, when spotted by one of the photographer's friends. "I was a girl with no money, lost, defenceless," she said. "He promised me a career as a model - big hotels, money, the chance to meet famous people. Above all, he promised that I would get out of the hostel."

On their second meeting, she said, Bourgeois persuaded her to undress for photographs which would, he said, launch her to stardom. He also seduced her. A few days later, the photographer took her to the home of his "friend", the French movie producer, Alain Sarde (producer of Paparazzi). She said that Bourgeois told her: "If he wants to go to bed with you, do it. It'll be good for your career in the cinema." She had sex with Sarde and was given F1,500 (pounds 150).

Nadia said she was "presented" soon afterwards to Robert De Niro but nothing happened; she said she was urged by Bourgeois to have sex with Fibak, but refused. That summer, she was packed off to Saint Tropez, where she was told her career would finally take off. Instead, she said, she found herself on a yacht - with another girl - performing sexual acts with the Qatari millionaire, William Kazan.

Bourgeois, an unkempt man with lank grey hair, who stood in court with the help of a cane, denied the charges of proxenetisme, or pandering (prostitution, as such, is not illegal in France). All he had done, he said, was "present" a few girls to his friends. Challenged by the court president to say whether he knew that Nadia was prostituting herself, Bourgeois admitted: "With Sarde, yes. With Kazan, I only knew later."

A Swedish girl, Julia, 16 at the time, also said that she had been taken aboard Kazan's yacht for photo sessions, where she claimed, she was sexually attacked. Bourgeois said Julia had gone aboard the yacht willingly and made no complaint at the time. Girls would be persuaded to have lurid photographs taken to circulate to film companies and modelling agencies. Instead, the court was told, Bourgeois would send folders of the pictures, on approval, to potential clients. If the girls refused to play along, they were warned that the photos would be sent to their families.

Even after the victims had been persuaded to prostitute themselves, the fact that the clients were often celebrities from the cinematic and fashion world helped to preserve the fiction that the women were climbing the ladder of fame.

Almost half the girls questioned by police had been promised a job modelling for the Clarins cosmetics company. Several girls claimed to have been taken to the office of the head of the company, Christian Courtin. "Bourgeois told me not to wear any underwear, because the lines would show," said Magadelena O. "Courtin asked me to undress and then touched my thighs and buttocks. He promised me a job in his next advertising campaign."

Sarde, a respected figure in French cinema, admitted in a written statement read to the court, that Bourgeois had sent him 17 girls while he was casting for Paparazzi in 1996. He denied any knowledge of promises made to the girls that they might get a part in the movie. "Bourgeois took advantage of my name ... as far as I was concerned, all the girls he sent to my bachelor flat on the Avenue George V came as prostitutes. The proof was that they all left with the FF1,500 agreed with Bourgeois."

One of the other defendants, Nazihabdullatif al Ladki, was a Lebanese businessman and former private secretary to Prince Fawaz of Saudi Arabia, brother of King Fahd. He admitted dealing with Bourgeois over a period of six years, in which the photographer provided a stream of girls for his employer. "It's something quite natural among Arab princes to want pretty girls," Al Ladki told the court. "It wasn't pimping."

When he visited Paris, Prince Fawaz would organise elegant soirees for his wife at the Hotel Crillon or Hotel Royal Monceau. In the meantime, Bourgeois would send two or three girls around to the Prince's three-storey apartment on the Avenue Montaigne, off the Champs-Elysees. "If he liked the girls, (the prince) would give them FF10,000 (pounds 1,000) each," said Al Ladki. He would also give "presents" to Bourgeois, including FF50,000 on one occasion.

The six-day trial has been equally disturbing for what it has not revealed. There has been no reference in court to the two, centre-right French politicians, mentioned as regular clients of Bourgeois (but not named) in the report of the investigating magistrate who unravelled the affair.

There has been talk of "other famous names" on the client list - including, allegedly, well-known figures in British cinema - but no attempt has been made to elucidate the matter. There has been no exploration of the fact, also mentioned in the investigating magistrate's report, that the French interior ministry and foreign ministry tried to have the entire inquiry quashed.

It has been suggested, in leaks from the magistrate's office, that the Bourgeois-Brumark operation became, briefly, a kind of state-approved broker, providing girls to assist French arms companies to sweeten their deals with Gulf clients. Since this kind of thing was bound to happen, the foreign ministry and security services reasoned, it was better that a "known" and closely watched call-girl service should be used. This reduced the risk of blackmail or "pillow leaks" of secret negotiations.

So why was such an apparently politically protected network prosecuted, when others are not? Paris, like London, has scores of alleged escort agencies. Part of the answer is obvious: the operation run by Bourgeois was a particularly nasty one of its kind. Most of the women provided were not fully consenting professional adults. Bourgeois and the three other defendants faced charges not just of pandering but "aggravated pandering".

Another part of the answer is that the case fell into the hands of one of a new breed of young, tenacious and publicity-conscious investigating magistrates, who have transformed the French judicial landscape during the past 10 years. A generation ago, a case with such political sensitivities might easily have become derailed long before it reached a French court: the wrong-doers would have been warned off, rather than prosecuted.

The investigating judge in this case, Frederic N'Guyen, seems to have taken a positive delight in ruffling the feathers of the rich, powerful and arrogant. He was able to resist the pressure from the centre-right government, in power until June last year, to bury the case. Once a Socialist- led government came to power, he was able to make more progress.

Even then, however, he was prevented by the public prosecutor's office from extending his inquiry to areas of political sensitivity, including the alleged use of prostitution in arms diplomacy. He was refused permission to pursue his investigation of the links between Bourgeois and a shadowy character called Paul Barril, who once ran the dirty tricks department in the Elysee Palace for Francois Mitterrand, and now runs his own security agency for Gulf clients.

N'Guyen was also ticked off by the public prosecutor's office - with some justice - for his highly publicised "arrest" of Robert De Niro in Paris, early this year. De Niro, who was never more than a witness in the case, admitted having sex with girls presented by Bourgeois, but denied paying for their services.

The whole affair has left the French legal system splattered with bad blood. N'Guyen's annoyance with what he sees as political interference by the parquet (the public prosecutor's office), was leaked to the French press. As a "punishment", part of his inquiries - the possible rape charges against Fibak and Sarde - were lopped off and given to a more docile investigating judge.

In an extraordinary summing up on Tuesday - even by the standards of baffling, French judicial mores - the duty public prosecutor, Pascal Le Fur, took even further revenge. He spent two hours attacking Judge N'Guyen, nominally his own colleague, before turning to his case against Bourgeois and the others. In an unprecedentedly savage public roasting, Judge N'Guyen - the man who first brought the whole affair to light - was accused by the state prosecution service of publicity seeking and "taking liberties with the law and penal procedure".

Where does all this leave us, pending the second trial in May of Annika Brumark?

The case has exposed how confused the borderline is between the casting couch and prostitution; how easily star-struck girls can be entrapped to serve the desires of wealthy men; and how arrogantly such men - none of whom have even appeared in court as a witness - can exploit such girls without scruple or question.

But the case has also left the uneasy impression that - if found guilty - Bourgeois and his alleged accomplices are convenient fall guys for a wider and more complex tapestry of politics, celebrity, arms-deals and vice.