A backbench campaigner for better education on HIV has called for improved guidelines for schools.

Labour MP Neil Gerrard called for action after a survey found that more than 50 per cent of children aged 11-15 were unaware that condoms could prevent HIV.

The report, commissioned by Marie Stopes International UK, also found four out of 10 believed it was illegal for children under 16 to buy condoms.

Only a third thought they know enough about contraception.

Sam Guy of Marie Stopes said: "Not only are young people unaware of the benefits of condoms but many are also too embarrassed to buy and use them."

But Walthamstow's MP, who has long campaigned on HIV and Aids, said the report was not surprising.

"Most people working in the field of sexual health believe a lot more should be done in schools," he said.

"We should be giving much wider guidance to schools about the things we'd like to see them cover."

He said the Department of Health's sexual health strategy had led to more happening at government level but more actually needed to be implemented.

Gerrard said the idea of one-off campaigns to highlight a particular issue would only reach a very small number of children.

"It's easy to forget that sex education is ongoing. It isn't something you only do once," he said.

"New children join schools every year so it needs to be done again and again and again."