Lady Warnock wrote to Dr Nick Maurice, a Wiltshire GP, in a gesture of support and revealed that her husband, Sir Geoffrey, was deliberately brought to a peaceful end 18 months ago.
Dr Maurice has been criticised for his actions but he is not under investigation by the police or the General Medical Council.
Lady Warnock was reported as saying that Dr Maurice treated her husband, a former vice-chancellor of Oxford University, when he was dying from a lung disease. She said she and her five grown-up children knew what the doctor was going to do.
"We all knew my husband was going to die and Nick told me he was going to make him better. When he said that we all knew what this meant - end his suffering and end his life. Nick changed the medication and probably gave him more morphine, thus ending his life two weeks before he would have died."
Dr Maurice recently wrote an article condoning euthanasia and confessed to having induced a "quiet and easy death" for two patients in the previous three months, for which their relatives had been grateful.
"I am doing what every other GP in the country is doing but because I was prepared to raise my head above the parapet it has provoked this debate," he said.Reuse content