Baroness Warnock spoke on the eve of a Commons debate on the Mental Capacity Bill, which critics claim will allow "euthanasia by the back door".

In an interview with The Sunday Times, she said: "I know I'm not really allowed to say it, but one of the things that would motivate me [to die] is I couldn't bear hanging on and being such a burden on people.

"In other contexts, sacrificing oneself for one's family would be considered good. I don't see what is so horrible about the motive of not wanting to be an increasing nuisance.

"If I went into a nursing home it would be a terrible waste of money that my family could use far better."

Warnock, 80, a Lords' cross-bencher who helped frame Britain's legalisation on embryo research, also suggests that parents of premature babies should be charged to keep them on life support machines if doctors write off their chances of leading a healthy life.

"Maybe it has come down to saying 'Okay, they can stay alive but the family will have to pay for it.' Otherwise it will be an awful drain on public resources," she said. Warnock sat on a Lords select committee which agreed on a ban on euthanasia in 1993, but last year she conceded that the law needed to be reviewed.

Warnock's views are of considerable significance as she sat on an influential Lords select committee that agreed on a complete ban on euthanasia in 1993. Last year, however, she and two other peers on the committee conceded that the law needed to be reviewed and backed a private member's bill permitting assisted suicide for the terminally ill.

Warnock has previously admitted that a GP enabled her own husband, Geoffrey, a former vice-chancellor of Oxford University, to die peacefully using morphine in 1995 after he was incapacitated by a lung condition.

She said that her volte face on euthanasia was also influenced by the case of Diane Pretty, who suffered from motor neurone disease and unsuccessfully fought a legal battle to allow her husband to help her take her life. "That really moved me to think we must change the law," said Warnock.

The bill gives legal backing to "living wills", enabling patients to refuse treatment in the event of their becoming incapacitated.

Claire Rayner, president of the Patients Association, has written a living will instructing doctors not to give her life-saving treatment if she is given only three months to live or suffers brain damage following a stroke. Her husband, Des, has written a similar document.

Rayner, 73, who supports the Mental Capacity Bill, has demanded in her will that a "Do not resuscitate" notice be placed above her hospital bed if she loses the ability to speak or write.

The former nurse and agony aunt said: "If I have brain damage because I have had a stroke, that would be absolutely awful. Not being able to express myself, to talk or write, would be just awful.

"If the doctors feel that my time has come and my life expectancy is no more than three months, I don't want them interfering. I don't want them taking any action if I have a cardiac arrest or if I have respiratory failure. I do not want to be resuscitated . . . it is my decision, not their decision."

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