Doctors have warned patients may be being put at risk by unregulated or ad hoc screening health checks.
The BMA says mammograms are not proven to benefit all
A British Medical Association report said patients should be particularly wary of tests which could be bought over the internet or via mail order.
And it warns ad hoc tests may do harm than good, either through false positive or inconsistent results.
The prostate cancer test and mammograms for women under 50 are two tests whose worth are questioned by the BMA.
An estimated £65 million was spent on private screening in the UK in 2004.
But while patients may pay for the initial screening, if a potential problem is discovered it is the NHS that picks up the bill for further tests, counselling and treatment.
The BMA says formal screening programmes, such as breast checks for women between 50 and 70, have been introduced because they have been proven to be of benefit in detecting disease.
But the BMA says there are numerous examples where screening is available without such strong evidence to support its use.
Research has shown for example, that mammograms in women under 50 may not detect small cancers, and that it involves a high chance of misleading results.
CHECKS CAUSING CONCERN
Kits bought over the internet or via mail order
Mammograms for women under 50
The prostate specific antigen (PSA) test
Whole body CT scanning
Electrocardiograms for people without symptoms of heart disease
This can lead to further invasive tests and to surgery in many women whose cancers might never have progressed during their lifetime.
The use of the PSA test, which is provided on the NHS, is also questioned by the BMA, which says it "cannot identify those who will die" and warns the treatment of prostate cancer "has side effects that can cause more problems than the disease".
Two thirds of men with high PSA do not have prostate cancer, while some men with prostate cancer do not have high PSA.
The BMA adds that no evidence exists to show whether treating localised prostate cancer does more good than harm.
Concerns were also raised in the report about whole body computer tomography (CT) scans for people without any symptoms - which can cause false alarms and involve significant doses of radiation - and electrocardiograms (ECGs) for people without symptoms of heart disease.
The report says unregulated screening can put patients at risk because of a lack of evidence they are effective, no quality control, poor follow up and insufficient information before and afterwards.
It also says pre-implantation genetic diagnosis (PGD), now carried out on embryos to see if they carry an inherited disease.
Some are concerned it could be used to create 'designer babies' by selecting gender or eye or hair colour, but the BMA says, due to the difficulties involved, PGD is only to be used by couples at serious risk of having a child with a disease, and "frivolous" use is unlikely.
It adds there are concerns about the use of information on genetic tests on adults by insurance companies, and says the current moratorium should be used to consider if such information should be treated any differently from other medical data.
Dr Vivienne Nathanson, the BMA's Head of Science and Ethics, commented: "There is no doubt that some specific screening tests have the potential to save lives but this does not mean that there are no associated risks.
"We want the public to be extremely wary of unregulated screening.
"People should be especially cautious about testing kits that can be bought through the Internet and mail order.
"The BMA is also worried that even with the existing major programmes the information about the benefits and limitations may be insufficient for patients to make an informed choice based on the harms and benefits of taking part."
Emma Taggart, of Breakthrough Breast Cancer, said: "We know that mammograms are not as effective in women under 50, as breasts are dense and harder to image. Only women at a higher risk because of their family history are entitled to mammography, in the absence of any breast symptoms, before this age."
Dr Chris Hiley, of the Prostate Cancer Charity, said: "There are major uncertainties about the ability of the PSA test to identify correctly men who have prostate cancer and exclude, correctly, men who probably don't have cancer.
"This is why the PSA test isn't available on the NHS in a screening programme and why we are urging the government to invest in research to find a better, more reliable test."
Professor Peter Weissberg, Medical Director of the British Heart Foundation said the organisation did not support the indiscriminate use of exercise testing to screen patients with coronary heart disease. "
I'm all for breast screening under 50. My mother was diagnosed with breast cancer 2 years ago, I asked to go on the mammogram list, after my GP messing me about and a pointless visit to genetic medicine, I was refused. I don't blame women for attending private screenings. When my mother used to attend chemotherapy there was a girl of 16 there who had had a mastectomy and reconstruction, another girl of 24 and one aged 28, and still we're being told it isn't common in young women. Who is kidding who? If I had the money I would definitely pay.
Natalie, Scotland, UK
The system of medical checkups in Britain, including screening, is inadequate. Everyone should be given an annual general check-up on the NHS, covering eyesight, hearing, cancer screening, heart condition, blood pressure etc. This is what happens in Japan. I am sure regular check-ups would save the government in Britain a fortune, and make the nation healthier.
J. Riley, Japan
Yes, I recently had a CT heart scan, which can detect early signs of coronary heart disease (this would normally require invasive procedures). In my case the results were very good but it did occur to me at the time that regulating this kind of testing might be necessary - otherwise it becomes an extremely effective way of queue-jumping within the NHS and the cost of providing such tests to any and every patient who wanted them would be far more than the NHS could possibly afford. It's another example of a key dilemma facing the NHS and which is not being addressed how do you limit or ration health services if they are all free at the point of use? The NHS is part of the civilised society which Britain is but these issues must be considered, rather than ignored as this government has been doing, if the health service is going to survive in the face of dramatic (and costly) medical advances.
My daughter was diagnosed with breast cancer at the age of 34. She found the lump herself, by which time she had three tumours and half her lymph glands were affected. We have to find a more effective way of screening young women for this devastating disease.
Yvonne Osman, Newark, Nottinghamshire
The demand for private testing (for all kinds of things and as with health care generally) is driven by the reality that patients often have real concerns - that a test will definitively answer, quickly - that the NHS is unable or unwilling to address unless you are happy to wait for months on end, by which time the problem may be untreatable. It is not at all obvious that "DIY" tests done using labs or other forms of private medicine are any less reliable than tests done by the NHS. Unless and until the NHS can provide the service people want, it is entirely reasonable that people will seek alternative and supplementary ways to get health care when it is needed, rather than in 9 months. Doctors, politicians and the NHS need to face this reality and find ways to allow patients to make use of what is available outside and inside the NHS in a complementary way, rather than whining that such and such a treatment should be their monopoly.