She is our philosopher queen. Whenever Britain is in a royal mess over some fiendishly tricky quandary, we beseech Queen Mary for her counsel.

And so it is that we head to her palace — well, a tiny cottage in a picturesque Wiltshire village of thatched terraces — to learn what she decrees on euthanasia. For not only is Baroness Warnock our pre-eminent medical ethicist who has sat on more committees than Frankie Dettori has horses — on subjects from vivisection to special needs children — she was also a wife and mother forced to decide what to do with an ailing husband.

As medical science advances, society is left bitterly divided over what to do with the terminally ill. A judge has just allowed a sick woman to travel to Switzerland to end her life and this Tuesday parliament will debate whether to give living wills statutory force — which critics have said is euthanasia by the back door. There are no easy answers.

So I head off to ask Mary Warnock for her words of wisdom — and, it turns out, controversy: for not only does she now think assisted suicide should be legal — before she didn’t — she also feels the very frail should slink away, like elephants, to die quietly. She reckons doctors, when asked to assist in this, bang on too much about their consciences rather than their patients’ interest.

Oh, and she suggests that if parents want to keep premature babies with unviable lives on life-support machines, they should stump up the cost. Gulp.

These are bracing sentiments, but then the baroness — one of whose earlier reports led to the legalisation of embryo research — declares firmly there is no place for spiritualism or sentiment in the law.

Over wine on a bitingly cold night by her crackling fire we mull over the dilemmas, and I feel much like generations of Oxford students in her tutorials: privileged, but nervous. For though Warnock is 80 and charming, she is sharper than a Jonathan Ross suit. Warnock explains that she has changed her public position on euthanasia because the public has changed its position.

But shouldn’t she tell us what to think rather than declare: “I’m their philosopher, I must follow them”? “I know it sounds Machiavellian, but I have come to believe in a distinction between personal consciences and public policy. If you change the law it must be enforceable.”

“People are much better informed than they were 50 years ago, so the more they are entitled to have their views heard. There is tremendous danger in thinking there are moral experts who know what is right.”

The public was moved on the euthanasia issue, she thinks, by the case of Diane Pretty, who died by suffocation as she feared she would, denied the assisted suicide she had campaigned for. “That really moved me to think we must change the law,” she says.

I agree with her wholeheartedly. I was the last journalist to interview Pretty and her husband and I came away from them wondering how anyone could look into those eyes of pain and deny them their final wish.

“She died in the way she most feared and that is appalling.”

And Warnock knows whereof she speaks. Her husband, Geoffrey, was saved at the last from a similarly gruesome death by what Mary considers a doctor’s mercy in upping his painkillers.