A study by Philip B. Stark, a professor of statistics at the University of California, Berkeley, has found that pornography accounts for just one per cent of all web pages.

The study was carried out after the American Civil Liberties Union (ACLU) took the US government to court over the Children's Online Privacy Protection Act.

The US Department of Justice commissioned the study as part of its attempt to get the Supreme Court to accept restrictions on internet use.

"One of the things we think came out of the government's study is that the chance of running into graphic content on the web when filters are on is extremely low,'' Catherine Crump, staff attorney at the ACLU, told the San José Mercury News, which obtained a copy of the report.

Stark found that around six per cent of searches referred to sites with sexual content, but suggested that this was mainly due to the high number of searches on sex-related topics.

Where blocking technology was used it tended to block such sites fairly effectively, but at the cost of blocking a lot of sites that had no sexual content at all.

In order to help with the study the US Department of Justice attempted to get search providers to hand over search histories of their users.

When Google ref used it was taken to court and forced to hand over 50,000 random web page contents from its index.