However, other Internet providers - including the largest, Demon Internet - insist that they will not block access to any discussion groups, and will delete specific images only if the police tell them to.
The issue, which has exposed a widening gap in the companies' opinion of the existing law on computer obscenity, could have a dramatic effect on the rapidly growing Internet community in Britain.
Under existing obscenity laws, including the Child Protection Act and the Obscene Publications Act, it is a criminal offence to store child pornography on any computer in Britain. Last Friday, Alban Fellows, a university researcher, was jailed for three years for running a child pornography library.
Technically, the managers and staff of an Internet provider whose computer systems contain newsgroups that include pictures of child pornography could be liable to arrest. Last week Shez Hammill, chairman of Britain's 49-strong Internet Service Providers Association (ISPA), told members: "If the police tell you about something and you don't do anything about it, then you are liable to prosecution and the confiscation of your equipment."
On Scotland Yard's advice, Pipex, the second-largest Internet access company, has deleted a "small number" of the discussion groups, or "newsgroups", from its computers. "We are filtering out a number of groups which are horrible," said David Barrett, the company's spokesman.
But James Gardiner, marketing manager of Demon, the oldest and largest of the British ISPs, with 65,000 users, defends its hands-off policy. "Our policy is that we are not responsible for putting it there. It's like the Post Office - they are not liable for the content of any package that's sent through the post. They are the carrier, and we argue that that is our role too." Demon, unlike Pipex, is not a member of ISPA.
The issue emerges because there are no checks on the source of data put on the Internet's discussion groups, or "newsgroups". There are roughly 16,000 newsgroups available globally on the Internet, which are for discussion and exchange of information.
Every day the users of the global network send roughly 2,200 megabytes of images or text to newsgroups, which are then passed internationally to other systems in the network. This means an image legal in one country could be passed to another where it is not.
Pipex, which has more than 10,000 users, is the second-largest ISP in Britain. It has been talking to Scotland Yard for about a year, and was advised of the offending newsgroups by the paedophilia and pornography squads.
The industry began only in 1992 when Internet connections became available outside academia. However, the legal ramifications of carrying pornography are unresolved. Mr Hamill said: "ISPA is negotiating with the police for concessions for this, so that they won't prosecute us for the odd occasion when we have something illegal - by accident - on our systems."Reuse content