The review will look at how professionals can help

And 35% of secondary teachers said 10 and 11-year-olds should get lessons on sex and relationships, a survey by the Times Educational Supplement suggested.

The poll of 2,000 teachers was published after schools minister Jim Knight set up a review of the subject.

He said too few youngsters were getting a good standard of sex education.

Sex education tends to focus on the biological functions rather than the wider issues around contraception and sexually transmitted diseases.

'Not acceptable'

Although some classes offer more detailed information in these areas, parents have the right to withdraw their child from them.

Mr Knight promised young people would be involved in drawing up a new policy, as ministers plan to work with the Youth Parliament on the issue.

Mr Knight said: "This review is a direct response to concerns raised by young people.

"We know that sex and relationship education is good in most schools but we know from talking to young people that in some schools sex and relationship education teaching is not up to scratch.

"This is not acceptable. I want to look at what the best schools are doing and make sure every school follows their lead."

'Specialists'

The TES survey found almost half of teachers had been asked to teach sex education, but three-quarters of those had received not training.

It also suggested that only one in 10 teachers thought parents would object to the subject being made compulsory.

The government review will also look at exemplar lesson plans and how best to use outside professionals in the classroom.