Soaring rates of sexually transmitted infections must be tackled by slashing the waiting times for treatment, the government's chief medical officer will warn this week.

With figures due on Tuesday expected to show another leap in cases of disease, Professor Sir Liam Donaldson will condemn 'unacceptably long waits' for treatment in his annual report. He will also call for measures to combat the spread of infection by identifying hidden cases of HIV that have previously gone undiagnosed.

David Hinchliffe, chair of the Commons health select committee, which last year published a chilling report detailing the sexual health crisis, said yesterday that Britain was still 'in the dark ages' when it came to sex and needed not just more treatment but better sex education.

'People desperately wanting help and advice and treatment are being turned away in their hundreds every week,' he told The Observer. 'But we were astounded at the complete ignorance of vast numbers of young people on what we would have thought was basic information in relation to their own sexual wellbeing. We are frankly still in the dark ages on sexual health and it's a very worrying scenario.'

Donaldson's report will show that nearly a third of patients with suspect symptoms have to wait more than two weeks for an appointment at specialist genito-urinary medicine (Gum) clinics. In some parts of the country, the committee found the wait was up to two months.

Health Secretary John Reid is expected to unveil tougher targets for waiting times at clinics in his public health white paper later this year.

Donaldson will also call for action to expose the hidden iceberg of Aids infection, with up to a third of HIV-infected patients in Britain unaware they have the disease. He is expected to say that in future anyone attending a sexual health clinic for the first time with symptoms of any infection should be urged also to have an HIV test.

GPs and clinics should recommend an annual test for gay men, while anyone who repeatedly picks up infections - a sign of frequent unprotected sex - should also be recommended to take the test. However, patients could refuse.

Donaldson is concerned that serious infections are being missed when patients attend clinics with the symptoms of other diseases. More than half of gay men with HIV are estimated to leave sexual health clinics undiag nosed, as do more than a third of African-born heterosexuals who are infected with HIV.

Experts have long warned that the struggle to get treatment helps to spread infection, as patients too embarrassed - or guilty, if they have been unfaithful - to tell their partners about symptoms continue to have unprotected sex before they can get an appointment.

The past six years have seen a 139 per cent rise in cases of chlamydia, which can cause infertility in women, and a 107 per cent rise in rates of gonorrhoea. Syphilis and genital warts are also on the increase.

Anne Weyman, chief executive of the Family Planning Association, called for a full programme of compulsory sex education in the national curriculum, covering not only the disease risk but the nature of relationships.

'We don't have the education we should have, and there are not enough teachers in secondary schools to provide it properly,' she said.

Children who learnt about relationships and making decisions as well as basic biology would be better equipped in later life to look after their sexual health, she said: 'The great majority of parents and children want more sex education, but you have this vociferous minority who are opposed to any provision at all, and who make life very difficult for the schools.'

Last night Andrew Lansley, the Tory shadow health minister, called for a new 1980s-style advertising campaign on sexual diseases, targeting the whole population rather than just high-risk groups such as gay men.

'You can't reproduce the Eighties campaign, but you do have to influence the population at large: they are still relatively ignorant about the rise in sexually transmitted infections,' he said.