This is a story about how one Belgian man single-handedly cracked an international child pornography ring. Or at least, it appears to be. The story goes like this: 9 June this year, and two men meet in Amsterdam. One is Robbie Van Der Planken, 23, a veteran of the local sex industry who started working in the city's boy brothels at the age of 12. The other is Marcel Vervloesem, a 46-year-old Belgian who heads the so-called Morkhoven Action Group, whose avowed aim is "to look for missing persons and to defend people who are discriminated against in the broadest sense of the word, using any means necessary". Vervloesem is searching for a boy who disappeared in Berlin in 1993, and who he believes is now working in an Amsterdam brothel. He thinks Robbie may be able to help him with his investigation.

Unknown to Robbie, Vervloesem is not alone. Other members of the Action Group are covertly watching the meeting. And they've noticed something odd - a stranger taking pictures. So they follow him, all the way to his home in the seaside town of Zandvoort. His name is Gerrit-Jan Ulrich and he's a 49-year-old computer salesman. He's also Robbie's longtime lover. Vervloesem approaches Ulrich and tells him about his investigation. Two days later, Ulrich calls the Belgian late at night and invites him over to his flat.

When they meet, Ulrich apparently tells Vervloesem that he is at the centre of an international child pornography network. In his flat he has five computers hooked up to phone lines on which he runs a bulletin-board service called Apollo. Punters dial up, pay a fee and can then gain access to tens of thousands of illegal photographs. He gives Vervloesem a computer disk containing 9,000 pictures, together with other disks which contain the names and bank details of Apollo customers from all over the world.

Why he suddenly chooses to come clean is uncertain. Ulrich is suffering from Aids and has only months to live. Vervloesem believes he wants to leave the network and start a new life. He also reckons Ulrich feels threatened by other members of the network and is looking for protection.

The next Vervloesem hears from Ulrich is when he telephones from Lyons. He and Robbie have fled together on a motorbike and are on their way to Italy. Ulrich says he'll give Vervloesem more material when he gets back to Holland - he's got a secret store under the floorboards in his living room. A few days later, on 20 June, Ulrich's body is found in a forest near Pisa. He's been shot several times and Robbie has been arrested by Italian police as the chief suspect.

Two days later, the Dutch police inform Ulrich and Robbie's families what has happened, and on 26 June they go to Ulrich's flat, together with his sister-in-law and a friend. The lights are on, and a computer is running. When the screensaver is deactivated, the screen shows an image of child pornography.

The women get the impression that the police are unconcerned, so next day they go back to the flat with Vervloesem. They force the door open; minutes later the police arrive. Vervloesem flees and the two women are detained. Later he informs the police about the secret stash and on 28 June they return to the flat, carry out a thorough search, and find computer records under the floorboards, including a list of 300 names which is said to amount to an international Who's Who of suspected paedophiles. It includes Warwick Spinks, who was released from prison in Britain last July after being convicted of drugging and kidnapping a 14-year-old boy, and is now believed to be in Prague, and Lothar Gandolf, a notorious German paedophile.

The Dutch police ask their Belgian counterparts to question Vervloesem formally. They search his flat and take away a computer. Vervloesem is led away screaming that he has been illegally arrested. Eventually he agrees to hand over his material to the Dutch and Belgian police in return for a pledge that there will be a thorough, multinational police investigation.

And then journalists come from all over the world to Marcel Vervloesem's modest council house in the small village of Morkhoven east of Antwerp to be told how he has cracked "one of the most extensive and violent child pornography rings ever discovered", as the Guardian puts it. "We've been fighting the police for years, but now this means our work has not been for nothing," says Vervloesem, basking in his new-found fame. In Germany, Chancellor Helmut Kohl immediately orders a nationwide offensive aimed at fighting child porn on the Internet. Austria, which currently holds the EU presidency, calls for action by the whole of Europe. It's a stunning victory for the little action group, who with scant resources have shown up the Belgian and Dutch police forces.

Well, that's the story that was reported. The truth, however, is a little more complicated.

When Marcel Vervloesem said he had been fighting the police for years, he was referring to the work of the Morkhoven group, which has feuded with the authorities constantly. Set up in 1990, the group at first focused on causes such as access rights for wheelchair users and the use of isolation cells in Belgian psychiatric units. Its methods have involved spectacular stunts aimed at attracting media attention. On one occasion Vervloesem invited TV crews to a local police station, promising he was going to turn it into a pigsty. When the cameras turned up and he was asked where the pigs were, he replied, "They're all here, but they're wearing uniforms."

Vervloesem's battles with the police earlier in his life, however, had received considerably less publicity, until the Belgian weekly news magazine Knack decided to investigate his past following the events of June. What they discovered was a long history of criminal activity and recidivism.

Vervloesem's record goes back to the Seventies. In November 1979, the criminal court in Antwerp found him guilty of the following charges: housebreaking, forgery, fraud, extortion, criminal assault on a minor and attempted arson. As a result he was forced to spend time in a psychiatric institution, setting a pattern that was to be repeated several times. In 1982 he was in trouble again, this time for setting up an illegal ambulance service with his common-law wife Elvira. It's said the main use to which he put his ambulance was to go shopping, making full use of the siren and flashing lights. In March 1985, he was found guilty of bouncing cheques to the tune of 96,000 Belgian francs (about 1,650 pounds) as well as fraud relating to unemployment benefit. More time in a psychiatric institution followed. Out on probation, he set up a company to help people with problems of a social or material nature. This involved charging them a fee for writing letters of complaint to the European Court of Human Rights. In 1986, he was convicted of threatening behaviour, fraud and staging a bomb hoax. In July 1989, when he was finally released, a confidential report by the psychiatric service described Vervloesem as a "fantasist" and stated that he would "probably always display unpredictable behaviour".

You could say that all this is history and has no bearing on Vervloesem's work with the Morkhoven Action Group. However, his most recent conviction is considerably more pertinent. Last April, he was convicted of extortion by the criminal court in Dendermonde and sentenced to two years in prison. One of the reasons the court gave for its decision was that "the defendant keeps abusing what are the essentially worthwhile objectives of the Morkhoven Action Group".

The case goes back to 1991, when Vervloesem was asked by a gay man in his twenties to recover some nude pictures of him from his former lover in the small town of St Niklaas. Vervloesem went to the man's house and demanded them, but at the same time, as the court was later to hear, he also demanded 120,000BF (about pounds 2,000) which was reluctantly handed over. The man then later told the police. Vervloesem has appealed against his conviction and the new hearing is due to take place in a few weeks' time.

Sitting in the front room of Vervloesem's house, I asked him about the extortion charge. Speaking in Flemish through an interpreter, he told me the accusation was false and compared his case to that of the Guildford Four. The people at the top in the Justice Department knew he was innocent, he told me. It was a grave miscarriage of justice. When it all comes out, there will be enormous political consequences. "The government has already failed the people once. If they fail again this time, there will be a political crisis," he said.

He was referring to the case of Marc Dutroux, a 40-year-old unemployed electrician who was arrested by the Belgian police in August 1996. At his house in Charleroi, police discovered hard-core paedophile videos; in a basement bunker he had built, they found two teenage girls who had disappeared in the preceding weeks. At Dutroux's main home just outside Charleroi, they found the buried remains of two eight-year-old girls who had been imprisoned by Dutroux but had died of starvation while he served a jail sentence for car theft. The remains of two more girls were discovered at the home of an associate.

Following Dutroux's arrest, it quickly became clear that the investigation had involved quite staggering levels of incompetence on the part of the police. Dutroux had previously been jailed for the rape and abduction of five girls in the mid-1980s. His mother had repeatedly warned the police that he was an incorrigible criminal, and an informer had told them that Dutroux planned to abduct and sell young girls. The informer told the police in the summer of 1993 that Dutroux was building a bunker at his house in which he was going to imprison the girls, but officers believed Dutroux when he said he was building a new drainage system. When officers went to Dutroux's home to arrest him for car theft in the autumn of 1995, they heard children screaming but accepted Dutroux's word that it was the voices of his own girls playing.

In October 1996, the investigating magistrate, Jean-Marc Connerotte, was removed from the case by the authorities because he had attended a fund-raising dinner for the victims' families. For the Belgian people, this was the last straw. Their dissatisfaction was symbolised by the so- called "White March", when over 300,000 citizens wearing white clothes and holding white balloons and roses marched in silence through the streets of Brussels. There was a general feeling that not only were the police and judicial authorities inept, but that Dutroux had friends in high places.

Although a parliamentary commission found no evidence to support the latter claim, there is still a general belief amongst the public that there is something rotten in the state of Belgium. When I asked Vervloesem why the Belgian authorities should want to obstruct his investigations, as he claims, he replied: "It has to do with certain people at high levels who need to be protected." In the current atmosphere of distrust, there are many who are happy to believe him.

As one Belgian journalist told me, "The justice department in general and the magistrates in particular have lost so much authority that people like Vervloesem are given a platform."

A peripheral figure in the extortion case against Vervloesem was the Dutch owner of a gay bar called the Gayata in the small town of Temse, not far from St Niklaas. The man was also suspected by police of sending underage boys to Holland to act in porn films. In preparing his defence, Vervloesem was allowed access to the file giving details of their investigation.

It described how in 1992 they had raided a gay party in Waalre at which guests were watching child pornography videos and engaging in sex with minors. Present at the party were Robbie Van Der Planken, Lothar Gandolf and a certain "Norbert DR" from Temse. The police discovered that Norbert DR was not only a collector of child pornography but had also made several short porn films with underage boys on the Portuguese island of Madeira in 1991.

Vervloesem was quick to jump to conclusions. He made a link between the Madeira films and what he called the "Temse network" which he claimed sent underage boys to Holland. Furthermore, the presence of the German Gandolf and the Dutchman Van Der Planken at the party in Waalre added another dimension. Suddenly the network was extending all over the world. "Internet child porn, kidnapping of children, sale of children" is how he describes this sinister international network. "Babies who get raped, children who are tied down and abused. Not the same as the usual child- porn milieu. What we are dealing with here are very serious cases indeed, where there is no respect for the children whatsoever and a child can be kidnapped from a street corner."

However, the police investigation of the so-called "Temse network" found that all the boys involved were over 16 and were properly paid for their work.

Comment: Oh that's ok then, they were all 16 and were just 'working boys'.

Christian Dufour, the local prosecutor in the town of Dendermonde who is currently investigating the Madeira case, told me: "I know that Mr Vervloesem pretends there is a Temse network. The only thing I know is that Norbert DR a few years ago had contacts with other people who were in the business of pornography. But a network? I'm not so sure."

"There's no reason why Norbert DR, having been involved in the Madeira tapes, is part of some other network just because he was in Waalre when the police raided the party," a Belgian journalist told me. "It's all more complicated than Vervloesem would like it to be. He's like a juggler with documents and disks and names and facts. He jumbles everything up."

Vervloesem's discovery that Robbie Van Der Planken was associated with the bulletin board in Zandvoort is for him the final proof of an international network linking Madeira and Temse to Holland, Germany and beyond. However, his detractors believe that his motive in making such grand claims is simply to boost his chances when his case goes to appeal. "He could divert attention from his own case by focusing on such a major case," a journalist told me. "He wants to prove he is the good guy who has been exposing networks and things like that."

At present, neither the Belgian police nor their Dutch counterparts are willing to comment on the progress of their investigations into the material which Vervloesem has provided. However, the German police have said that the pictures to which they have been given access in their own investigation are several years old. The unofficial word is that the same applies to the pictures in the possession of the Belgian and Dutch police, and this would not be surprising. Most of the pictures found on such bulletin boards are duplicated on many other similar sites and can date back years.

Comment: Nothing to see here folks, the images were all several years old, it's all in the past now...

"For sure, the pictures show people raping small children, but how old is this material?" says Marc Helsen, a reporter on the daily newspaper Het Nieuwsblad who has reported on Vervloesem's activities for some years. "Some specialists say it's 10 years old and has been copied over and over and over again, which means the people in Holland were just copying the pictures. The question is whether there were films and photographs being made in the last couple of years."

Comment: It's just pictures of infants being raped from like ten years ago, get over it...

So far, it seems that all Vervloesem has uncovered is a bulletin board showing images of child pornography. This is, of course, something for which he should be congratulated, but it is still a long way from an international conspiracy by paedophiles to kidnap children and exploit them against their will. It is also a far cry from the so-called 'Wonderland Club', a paedophile ring which was recently busted in an international operation co-ordinated by Britain's National Crime Squad. Considerably more sophisticated than a bulletin board, the club was based at an encrypted site on the Internet, and a condition of entry was that each new member was required to provide 10,000 new pictures.

"Vervloesem triggered the investigation, and you have to give him credit for that," says Helsen. "But then he withheld the evidence from the Belgian police. The trouble with Mr Vervloesem is that he kind of likes publicity and all the attention he gets and it tends to steer his actions. There are questions about his reliability, and his methods."

"So is he a hero?" I asked.

"Oh not at all, no," he replied, and laughed.