Thirteen suspected paedophiles were arrested and 27 computers seized in police dawn raids Wednesday in the UK's largest ever police operation against child pornography on the Internet. Videos, CD-ROMs and thousands of paedophile pictures -- which included images of children being sexually abused -- were also seized in raids in both England and Scotland. Those arrested reportedly included the housemaster of a Leicestershire public school. Forces in Grampian, Derbyshire, Merseyside, Humberside, Hertfordshire, West Yorkshire, Somerset, Bedfordshire, Lancashire, Devon, Cornwall, Sussex and London took part in the raids, codenamed Operation Janitress. Police had worked with Internet Service Providers (ISPs) to track down some of those arrested. Operation Janitress was the result of a two-year investigation, which began after a Gloucestershire man was arrested for the suspected abuse of his children. Police learned he was in contact with a London man who was allegedly running an online child pornography swap club. DCI Bob McLachlan, head of the Met's Paedophile Unit, explained that Wednesday's arrests were the result of an intelligence-led operation targeted at stemming the distribution of child pornography via the Net. McLachlan claimed that those who possessed such material were themselves guilty of child abuse. "Images like these are evidence of the sexual assault and rape of children -- and anyone who buys or downloads them perpetuates the cycle of abuse," he said. He explained that while the use of the Web to disseminate paedophilic images was increasing, the police were developing new methods to combat the problem. "We know that the Internet is increasingly used as a conduit for the exchange of pornographic pictures of children. Those responsible believe that the Internet affords anonymity, but police technology in this area is increasingly sophisticated," McLachlan warned. Last week, seven men pleaded guilty to their participation in what was then the world's biggest Internet pornography ring to be uncovered. Those arrests came as part of Operation Cathedral, a massive international police operation involving 12 countries. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet News forum. Let the editors know what you think in the Mailroom. And read what others have said.