Their call came as the British Medical Association made it clear that no doctor should strike off families refusing to allow toddlers to have the controversial measles, mumps and rubella (MMR) vaccination.

The research team, psychiatrists from Grovelands Priory Hospital in London, were worried that GPs were striking off large numbers of mental patients - but could not find a health authority willing to give them any information.

At Grovelands, they found that among 50 mental patients, 15 had been struck off by a GP.

They also had concerns that GPs worried about meeting tough government targets on immunisations, or cervical screening, might try to throw off patients who refused to take part.

If the GP meets the target, he or she will receive extra money, but even if the target is missed by a single patient, nothing will be paid.

Health authorities, says the research team, should collect all the necessary data to make sure family doctors are only removing patients from their lists in the correct circumstances.

Last resort

The House of Commons Public Administration Committee has said that patients should only be dropped as "a last resort" - and that it believed that patients were unfairly removed "more than occasionally".

GPs are entitled, under the terms of their contract with the NHS, to remove any patient they want from their list - just as patients are free to change doctors whenever they wish.

However, both the British Medical Association, and the Royal College of GPs (RCGP), which sets standards for the profession, say that patients should only be struck off when the doctor-patient relationship has "irretrievably broken down".

Examples of this, say the RCGP, include a patient who is violent or threatening to the doctor, or who moves out of the area.

Dr John Chisholm, chairman of the British Medical Association's GPs committee, restated advice they issued to GPs in June.

He said: "The GPC does not support or condone the removal of patients solely because they have made a complaint, or because their treatment is too costly, or because they are suffering from a particular clinical condition.

"Nor would it condone removing patients from lists in order to meet target payments."