Some campaigners fear that such advice could pave the way to legalised euthanasia.

And in some cases, it says such treatments can be stopped even for patients who are not about to die.

One barrister who specialises in medico-legal issues, Jamie Bogle, told the BBC: "What these guidelines will do is widen the cases right out to a broader range of conditions and diseases beyond simply Persistent Vegetative State - many of them non-terminal.

Jamie Bogle says doctors could be obliged to remove treatment

"Doctors will be obliged to terminate food and fluid, and that's intentional killing, and I don't think anybody wants that."

But the advice stops well short of any encouragement to commit euthanasia - doctors actively giving treatment to hasten or bring about death. That is still illegal under UK law.

Dr Michael Wilks, chairman of the BMA's Ethics Committee, which drew up the guidance, said it would encourage a "compassionate" approach by doctors.

Fergus Walsh reports: "Doctors can decide to withdraw feeding tubes"

And committee member Professor Raanon Gillon, a GP and medical ethics expert said: "This is not about euthanasia, it's about an intention to withdraw useless or non-beneficial interventions."

The guidance says: "It is not an appropriate goal of medicine to prolong life at all costs, with no regard to its quality or the burdens of treatment."

The most controversial area addressed by the guidance is what to do with patients who are no longer capable of telling doctors what they want.

Nutrition and even water, if they have to be given medically, are legally counted as treatments in England and Wales - and can be withdrawn in certain circumstances.

The BMA says doctors should have the final say over whether treatment, including feeding and giving water, is in the patient's best interest.

Only in cases where there is a dispute between relatives and doctors should the courts be consulted.

But the guidance makes plain that such weighty decisions should not be rushed, and that second opinions from experts should be sought.

This particularly applies to patients in suffering conditions such as "Persistent Vegetative State" (PVS), where although there is extensive brain damage and little or no chance of consciousness, the patient can be kept alive indefinitely.

A legal battle raged over Hillsborough victim Tony Bland

It was in the case of Tony Bland, a victim of the Hillsborough football disaster left in PVS, that Law Lords decided that feeding did constitute medical treatment and could be withdrawn.

Following the landmark ruling, there have been 18 cases brought before the English and Welsh courts by doctors or relatives asking to withdraw food or water from comatose patients.

There is no legal requirement to do this in Scotland.

Patients who have instructed their doctor to stop treating or feeding them should be respected, says the guidance.

Parents should be able give or withold such consent on behalf of babies or young children - and the doctor should follow that unless convinced it is not in the child's best interests.

Spare patients' suffering

But the BMA hopes the set of rules will give GPs and hospital doctors more confidence in dealing with the terminally-ill, and not continue with painful treatments simply because they are afraid of the consequences of stopping.

Dr Michael Wilks, chairman of the BMA's medical ethics committee, said: "Some people believe passionately that life must be preserved at all costs, but most people and certainly the majority of doctors accept there comes a point when treatment ceases to be of benefit for the patient.

"Death cannot be postponed indefinitely. There comes a point where medical treatments, including artificial nutrition and hydration, are more of a burden than a benefit to the patient."

But Michael Willis, of the anti-euthanasia Pro-Life Alliance, said: ""This is a benchmark recommedation in terms of the introduction of involuntary euthanasia into this country. Involuntary euthanasia will become accepted practice in the hospitals of the UK."

Jenni Burt of the Voluntary Euthanasia Society said the guidelines were "very sensible", although they were not directed at introducing euthanasia.

Instead, they would be invaluable at letting doctors know where they stood, she said.

"A doctor in one area may be happy to withdraw artificial feeding from a severe stroke victim who's not going to recover," she said.

"But in another area a patient in the same position may be artificially kept alive for months or even years because that doctor is uncertain about where they stand.