Results from the check-ups varied from company to company and could raise alarm unnecessarily or provide false reassurance, undercover researchers found.

One researcher was given conflicting advice by three leading firms on his risk of heart disease despite getting almost identical results.

And companies that offer CT scans could be exposing patients to unnecessary and harmful radiation.

A survey of more than 4000 Which? members found that three in 10 would consider a private health check and most said they would do it to set their mind at ease.

Which? researchers aged 46 to 62, with no known health problems, paid 12 visits to six healthcare companies -- Bupa, Nuffield Health, BMI Healthcare and three independent firms -- and paid an average of £423 to each for comprehensive health MoTs, not including scans or X-rays.

In eight cases, researchers -- none of whom had a major problem identified -- were advised to get further GP tests within six months.

The report also criticised the companies tested for failing on some occasions to discuss the downsides of the testing such as false alarms.

Martyn Hocking, editor of Which?, said: “Health MOTs often cater for the ‘worried well’ who want the reassurance of a clean bill of health, but they can pay hundreds of pounds for what sometimes amounts to little more than lifestyle and dietary advice. A false sense of reassurance is potentially risky, and if the tests flag issues that turn out to be false alarms, you could actually end up with unnecessary worry.”

Which? advises people who are considering a health MoT to check what information, tests or screening are available from their GP first, and to see their GP if they have symptoms.

Dr Peter Mace, assistant clinical director at Bupa, said: “Any doctor will tell you that the earlier a health problem is identified, the more likely it is to be successfully treated. That’s why it is so important that health assessments are carried out professionally by appropriately trained doctors.

“We agree it is wrong to provide false reassurance or unnecessarily worry people with tests which may not be backed up by clinical evidence. This is why we ensure that people are told about the risks and benefits of all the tests they have beforehand.

“We see people interested in their health who want to take positive steps to improve it and understand their own health and risks.

“We do not offer or support whole-body scanning. We believe these can find problems of uncertain significance that worry people rather than reassure them”

A spokesman for Nuffield Health said: “Health is more than just the absence of disease. As a result, a significant percentage of our health assessments focus on

energy management, immunity, stress management, sleep and libido -- areas that could be described as ‘general vitality’. Much of the advice we give is about lifestyle areas they should think about changing. Our concern is that some companies offer expensive tests -- such as whole body imaging -- without good evidence that they need to be carried out in the first place.”