The British Medical Association says patients may be wasting time and money by paying for tests such as breast cancer screening and whole body CT scans. Patients spent £65m on screening last year in the UK, and the market is expanding.

But the BMA warns that unregulated screening, which often gives unreliable results, is diverting scarce NHS resources away from the genuinely sick and increasing anxiety for screened patients.

Dr Vivienne Nathanson, the BMA's head of science and ethics, says private tests often identify problems that will never develop into a major health concern. This can result in invasive tests, serious surgery and increased anxiety for patients.

The BMA's report, Population Screening and Genetic Testing, highlights the difference between private screening of apparently healthy people and formal screening programmes supported by the NHS.

It warns that whole-body CT scans, offered by some commercial companies, cause many false alarms.

Public health consultant Dr Steven Laitner said: "Some people may have lung surgery thinking they have had cancer picked up early by having the scan but they may never have developed lung cancer."

He said that a CT scan had 100 times the dose of ionising radiation as a chest X-ray, and at these doses around one in 2,000 people could develop a fatal cancer.

The report says mammograms are useful in detecting breast cancer in women aged 50 to 70, as offered by the NHS programme. But there is no evidence that they are of use for under-fifties.

The prostate-specific antigen (PSA) test for prostate cancer can give similarly misleading results. Two-thirds of men tested with high PSA do not have prostate cancer.

The report highlights the importance of recognising the implications of genetic testing. Dr Nathanson says it is vital people are not excluded from insurance because of genetic tests, especially as tests are developed for more conditions.

A Department of Health spokesman said: "Patients who have concerns about genetic diseases should seek advice from their GP who can then refer them to specialist genetic services if this is appropriate."

The private health provider Bupa agrees that everyone who has screening should be fully aware of the risks and benefits.