Today's parents might have grown up as the first generation for which pot, the pill and promiscuity were perfectly normal. But they are as hopeless as ever at talking to their own children about sex.

A new study shows that a third of parents think that the most likely reason for a teenager to seek advice or call a helpline is to discuss physical or emotional abuse. But almost half of 25,000 children who sought advice were seeking the most basic information about pregnancy or sex.

'There appears to have been so much concentration on issues such as bullying and homelessness and drugs that many people have overlooked the things that most children are still worried about,' said Mark Frankel of helpline Get Connected, which commissioned research among parents and children around Britain. 'There is still huge ignorance about things like contraception.'

Bullying is the main issue in just 6 per cent of calls to the helpline over three years. Only 3 per cent were from young people who want to talk about drugs.

Just one in 50 parents thinks their teenager might need outside information or support about sexuality. But one in three adolescent boys out of 8,000 who called the helpline was worried about their sexuality. The figure is five times higher than calls about drugs and bullying put together.

'Boys who call us about sexuality are monosyllabic and uncertain,' said Frankel, a volunteer on the Get Connected switchboard. 'They are still terribly frightened and feel unable to talk to people at school or at home. They simply say they can't speak to their parents and are often unable to say they are anything more than terribly frightened.'

Four out of five parents told researchers they were comfortable talking to teenage children about almost anything, including mental health, abuse, sex and pregnancy. But only one in three children said they were happy to talk to parents about sex, pregnancy, sexuality or abuse.

The consequences of basic ignorance are clear. Britain's overall rate of teenage pregnancy remains the highest in Europe. Among under-18s, there were more than 41,000 pregnancies in 2000. Figures from the Office of National Statistics suggest that the trend is falling slightly. However, among under-16s there were 8,000 pregnancies, up 161 on the previous year in spite of concerted efforts to address the problem.

There is also a widespread fear among some doctors that sexually transmitted diseases are on the rise because of a failure to address sex education adequately. Parents can still demand that their children do not take part on religious grounds and many teachers reportedly feel constrained from talking about HIV because of Section 28 of the Local Government Act, the controversial legislation which forbids the 'promotion' of homosexuality. Research in schools last year found that 40 per cent of 11-year-olds had never heard of Aids.

Researchers commissioned by Get Connected analysed all 25,000 calls made since the helpline was set up in 1999 as a guide to sources of advice and support.

'In spite of schools and society being more open about sex and sex education, parents feel more and more isolated from their kids as the nuclear family breaks up,' Frankel said. 'One of the key things we can do with young people is to encourage them to talk to people they already know.'

ben.summerskill@observer.co.uk