When seven British paedophiles belonging to the “Wonderland Club” were jailed in 2001, they and their 180 fellow members were said to be part of the world’s biggest group of online abusers.

The operation that led to the conviction of Philip Thompson yesterday is expected to identify 10,000 users of the internet forum of which he was a key moderator and administrator.

The seven members of Wonderland had traded 120,000 images. Thompson had more than twice that number stored on his computers. Although the scale of the online paedophile problem appears to be growing and a significant number of abusers evade justice, law enforcers are not in complete despair.

In 2001 the lament from police trying to grapple with the most horrendous area of the developing world of e-crime was that by the time they caught up with the technological trickery of one paedophile ring, another would be using more advanced methods of encryption and disguise. However, massive investment, pioneering techniques and strong international co-operation has tilted the battle back in favour of the investigators. Highly trained officers routinely go online posing as child abusers eager to gain access to members-only chat rooms where the worst imagery is exchanged.

Last year investigators arrested the kingpin of one network while he was online and took over the running of his site for ten days to amass evidence against hundreds of suspects.

Techniques developed in the fight against terrorism or organised crime are increasingly deployed — including physical surveillance of dangerous paedophiles.

For the men and women involved, this is a zero-tolerance area of crimefighting. They even demand that no one uses the words “child pornography” in relation to the harrowing images that they find. Every photograph, they emphasise, captures an actual situation in which a child has been abused.

Times Recommends

• Oh no, Mr Darling: you have failed
• BBC survives dogfight over Kennel Club expose
• Where the Rosetta belongs can’t be set in stone