This club had its own chairman and treasurer. Its business was child abuse

It seemed like an ordinary club, with a chairman, a treasurer and a board of long-serving and respected members.

Everyone had a nickname and there were the usual petty rows: grumbles that too many members were being allowed in without going through the official channels or being approved by the hierarchy.

But it was the sinister entry fee that exposed the fact that this was no ordinary club: each new member had to supply 10,000 pornographic images of children.

This was the Wonderland Club, an international online paedophile ring which ran for four years before finally being smashed by the biggest international police operation ever undertaken.

Tomorrow, seven British members of the ring will be sentenced at Kingston Crown Court for 'conspiring with others to distribute indecent images of children'. The legal jargon masks a terrible reality: Wonderland was an international network of paedophiles involving the rape of boys and girls live on camera and the traffic in images of the torture of children as young as two months.

The international investigation to crack the ring was the biggest in policing history, taking in 13 countries and 180 men. Led by British officers, on 2 September 1998 police forces simultaneously kicked in the doors of 107 homes and made 104 arrests.

The suspects included the usual collection of outsiders: unemployed loners in UK bedsits, a father and son in a US trailer-park. But they also numbered a computer consultant in an Italian penthouse apartment, a German professor and a Canadian medical student who had trained on a children's hospital ward. The more senior members of the club earned their status by providing photographs and videos of themselves performing sex acts with children. In a perverse paedophile version of Hollywood, certain children became 'stars'.

One prolific abuser, Gary Salt, invited other members to visit his Stockport home to pose with children in front of the webcam as if they were meeting a screen hero. Thesheer weight of the physical evidence illustrates the enormity of Operation Cathedral - 750,000 individual images of children and 1,800 computerised videos depicted children being sexually abused.

The images were so appalling that National Crime Squad officers who had to sift through the mountain of material had compulsory therapy sessions to help them deal with what they saw.

'These really are quite horrific images,' said Alex Wood, deputy chief inspector of the NCS. 'These are kids being subjected to the most serious, serious, abuse.'

The ring began to unravel after the arrest of Ronald Riva in Greenfield, California. Officers discovered that Riva had raped his daughter's 10-year-old friend in front of a camera which relayed the live image onto the internet. The child, who had been invited to a slumber party by Riva's daughter, is one of only two of the 1,236 Wonderland victims to have been traced. The other, a Portugese boy, has disappeared and police fear he may have been murdered.

Among six men who had typed messages of encouragement to Riva was Ian Baldock, a 31-year-old computer consultant from St Leonards, East Sussex. The FBI informed the UK police, who soon realised the scale of the enterprise they had stumbled on. Operation Cathedral was born.

'At first there was not enough police knowledge or power,' said Wood.

'We had to bring in computer experts who worked with us for 14 months. Once we had traced actual computers we then had to establish who was using that computer at a particular time and with many of them in libraries and universities it wasn't easy.'

Round-the-clock surveillance on suspects had to be introduced to ensure none had access to children while the investigation was ongoing. At one point, the operation almost collapsed when one British man, Gavin Seagers, was discovered working with Sea Cadets. The police knew that if they arrested him they risked tipping off the whole network. Tracing the victims of the Wonderland Club is now a priority. New technology is being tested out by Interpol based in Lyons, France, to enable photographs sent in by social services and families to be 'matched' by computer against the victims' photographs. Already 900 children have had their photographs 'sanitised' and stored and police forces across the world will be able to access them.

The British Government introduced legislation last month to increase maximum sentences for the possession of child porn from six months to five years. Those caught producing or distributing the images will now receive sentences of 10 years rather than the present maximum of three. But the new sentences will not apply to the Wonderland Club.

Next month the internet Crime Forum at the Home Office will publish a report on chatrooms where child abusers discuss their fantasies. Police have become concerned that these forums are being used to 'groom' children and lure them to meetings with paedophiles. The report is likely to make depressing reading. A Home Office spokesman told The Observer : 'We have a very co-operative relationship with internet service providers, but it is technologically impossible for them to stop this stuff.'

In April, a new cyber-crime unit will start work involving 80 officers from the police, Customs and the National Criminal Intelligence Service.

According to the National Association of Probation Officers most internet offenders do not see themselves as criminals and few receive treatment. Spokesman Harry Fletcher said: 'We are only beginning to understand the scale of this crime. It is a major problem that their offending behaviour is not being challenged.'