The eating disorders charity, B-eat, told the BBC little progress had been made on combating "pro-ana" sites that provide easier access to information on how to lose weight.

B-eat and health experts say internet sites play a significant part in providing easier access to information on how to get thin, and highlighted support groups on social networking sites such as Facebook and MySpace.

A doctor at one of the country's largest eating disorders treatment centres told the broadcaster social networking sites should act more responsibly.

But the websites say they are working with campaigners, although that it can be hard to distinguish between support groups and "pro-anorexia" groups.

Susan Ringwood from B-eat said groups on social networking sites encouraged people to avoid treatment for eating disorders. She told the BBC: "They have acted to remove other content that is seen as 'dangerous', or could encourage young people to do dangerous things."

Dr Ty Glover, consultant psychiatrist on the Eating Disorders Unit at Cheadle Royal Hospital, told the broadcaster: "Social networking sites can censor their material and we expect them to act responsibly.

"We are horrified at the content of these sites and the tips they give on how to be thin. People with eating disorders are extremely vulnerable and often have very low self esteem, so pro-ana and pro-mia sites can be very damaging as they are sending out the wrong advice."

A spokesman for MySpace said that rather than censor support groups for users it wanted to create partnerships with organisations such as B-eat.

A spokesman for Facebook told the BBC: "Many Facebook groups relate to controversial topics; this alone is not a reason to disable a group. In cases where content is reported and found to violate the site's terms of use, Facebook will remove it."