Dr Michael Irwin, a retired Sussex GP and former medical director of the United Nations, and Dr David Moor, a GP in Newcastle, defended their actions in prescribing lethal doses of painkilling drugs to the patients on the basis of the principle of double effect.
That principle states that it is permissible to administer drugs without limit to terminally ill patients, even though they may shorten their lives, provided the intention is to relieve suffering and not to end life.
Mercy killing amounts in law to murder, because of the clear intention to end life. It means too - assuming the action is revealed to the police, can be proved in court beyond reasonable doubt and that the jury is willing to convict - that a judge must impose a life sentence.
Dr Irwin, who claims to have helped 50 patients to an easier death over a 40-year career, said the doctrine of double effect was full of hypocrisy, with doctors expressing surprise that their patients should die after receiving massive doses of drugs. "It can often be regarded as a form of slow euthanasia. I would like to see doctors becoming more honest about their real motives for applying this practice."
He denied placing a plastic bag over the head of one patient who was suffering from motor neurone disease, saying she had acquired the bag and used it herself. He admitted advising another patient what dose of morphine would be fatal but said he had not prescribed the drug.
Dr Moor, who claims to have helped 150 people to die, dismissed as "twaddle" calls by the British Medical Association for him to be prosecuted for murder. "I am working within the constraints of what we can do, and those constraints mean we can relieve suffering," he said.
Northumbria police said they were investigating Dr Moor's claims. Sussex police said they were not investigating Dr Irwin but was in discussion with the Crown Prosecution Service.
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