A leading specialist has launched a broadside against the medical screening industry for peddling unproved procedures that cause more harm than good.

Professor Nicholas Wald, the director of the Wolfson Institute of Preventive Medicine in London, says hi-tech screening services which promise to detect early signs of heart disease, cancer and other conditions are being promoted by commercial organisations as a dubious way of reducing health risks. Clinics offering body scans, virtual colonoscopies of the bowel, and mole assessments for skin cancer have sprung up around the country charging up to 1,000 per test.

One firm advertises its scans as an "MOT for the body". The scans have become fashionable gifts for people reaching milestone birthdays of 40, 50 or 60.

But critics say the scans often reveal abnormalities without being able to distinguish those that indicate serious disease. Many patients then need further checks, causing them sleepless nights with anxiety before they are cleared. At the same time, the scans deliver a hefty dose of radiation.

Professor Wald says insurance companies who promote medical screening to provide "peace of mind" are among the worst culprits. Writing in the Journal of Medical Screening, Professor Wald says: "Screening is usually a weak means of providing reassurance because [it] generally misses most cases of the disease for which [it] is carried out ... there is always some harm which is only acceptable if there is also some benefit," he says.

He singles out for criticism Saga Insurance, the group that targets the over-fifties, which wrote to customers last August offering them the chance of a CT scan to "look inside the body" and other tests for an all-inclusive price of 530. The scans are provided by Lifescan, a private health company.

Professor Wald warns that unless the industry cleans up its act, statutory control is likely.

John Giles, the medical director of Lifescan, said: "The science is very much on the side of screening. This is more a political, than a clinical, debate."