INTERNET filtering systems can’t block pornographic and other potentially dangerous materials, the National Association of Schoolmasters Union of Women Teachers has warned schools.

The union unanimously backed action to protect pupils and teachers from the perils of the Net at its annual Scottish conference last week in Seamill, North Ayrshire. Parents could accuse teachers of lack of supervision if extra checks are not built in and clear guidelines given.

John Milgrew, Holyrood Secondary, Glasgow, said his school, the largest in Scotland, had 2,077 potential users with access to the Net monitored by a company in East Kilbride. It was difficult to trace dubious connections.

The confusion was highlighted for Mr Milgrew when he tried to access the Daily Record but was denied. “There were particular words on the front-page that day which were the target for the filtering system. But children accessing an entertainment site got specific instructions and diagrams on how to inject themselves with heroin,” Mr Milgrew said.

Children’s work with computers was “quite superb” and the Internet was a “wonderful teaching tool” but there were obvious dangers.

Ian Wishart, Edinburgh, said he was looking at a school site, clicked to other links and in two moves had information on how to grow cannabis and roll cigarette papers. “The program that is meant to filter this out did not work,” Mr Wishart protested.

“Huge anomalies” in the Firewall filter program meant the city’s efforts to crack down on danger sites were compromised. There were no national guidelines to fall back on.

“Teachers who let pupils look at materials could be at risk,” Mr Wishart said.

Ian Clydesdale, Renfrewshire, called for a system of indemnifying teachers if something went wrong. Mr Clydesdale warned: “It’s the parents who should take most responsibility. We really need a crusade to make sure we raise concerns among parents. Pupils are not going to find out very much in school but when they are at home they will find out whatever they want to find and bring that knowledge into schools.”

Bruce Kerr, Dumfries and Galloway, a computing teacher, said: “If you’re into astronomy and look up Uranus, you’re in for a shock.” Monitoring systems were unable to protect pupils and teachers.

Mr Kerr advised teachers to ensure pupils logged on with their own name and password. Staff could then print out all the contacts pupils had made and if necessary send the list to parents.