They helped the patients die by either administering a lethal dose of drugs or withholding treatment.

A confidential Sunday Times survey of 300 doctors also found that more than two-thirds of doctors want the power to give patients lethal injections on request.

The findings come as the British Medical Association (BMA) prepares guidelines for doctors on when they should withdraw or withhold treatment from terminally ill patients.

At the moment the association does not condone euthanasia, but it admits that doctors are confused about what they can do if a patient asks for help to die.

Types of euthanasia

There are various forms of euthanasia:

• Passive euthanasia - life-sustaining treatment is withheld.
• Physician-assisted suicide - a patient is provided with drugs that will shorten life.
• Active euthanasia - a doctor administers life-shortening medication.

One in seven of the respondents to the Sunday Times survey said they had been assisted patients in committing suicide.

On average they had helped five patients to die.

Applying its findings to the UK's 36,000 GPs, the paper estimated that 27,000 patients had died with the help of their family doctor.

The BMA is drawing up a national code of practice after its own research found that doctors are already withdrawing or withholding treatment without the benefit of a rigid structure of medical rules.

Framework

Dr Michael Wilks, the Chairman of the BMA's medical ethics committee, said: "There is confusion. We do know doctors withdraw and withhold treatment.

"But doctors do not have a clinical or legal framework within which they can make these decisions. That is why we are taking urgent steps to draw up guidelines on this issue."

The rules, which will look at the withdrawal or withholding of treatment but not active participation by doctors in a patient's death, are due to be published by early 1999.

Doctors who help assist in a patient's death could face up to 14 years in prison under the 1961 Suicide Act.

But patients suffering from painful terminal conditions are known to have asked doctors to assist in hastening their death.