In 1992 Dr Nigel Cox was found guilty of the attempted murder of his terminally ill patient, Lillian Boyes. Patrick Boyes, the woman's son, thanks him
my mother Lillian was the life and soul of our family. She was always bright and never complained, even when she was doing back-breaking work on my father's farm. And when she began to suffer from rheumatoid arthritis her attitude didn't change. Her favourite saying was: "There are a lot of people far worse off than me."

After I got married and moved out, I still saw mum four or five times a week. We were very close. When my father died, mum's symptoms worsened. This was followed by the deaths of her sister and her brother. The cumulative stress seemed to compound the problem. But mum still wouldn't make a fuss, and because she seemed so resigned to her illness she helped ease the pressure on all of us.

Mum was in and out of hospital and between her visits we attempted to care for her. But when we reached the point where we couldn't lift her because she was in so much pain, we knew we couldn't cope anymore.

Mum had developed a painful inflammation of her blood vessels called vasculitis. A metal screw used to mend her fractured hip had become infected and a boil on her hip was constantly discharging. She was slowly losing her sight, although she tried to fool us to the contrary. And she was suffering from heart failure.

We came to realise there was a limited amount of time left for her and she knew it too. When my brother referred to "next summer" in conversation one day, she said: "There's not going to be a next summer for me. Let's be realistic." She wasn't being bitter or feeling sorry for herself, she was just bravely facing up to the truth. But at the same time she was determined to keep going for as long as she could.

In hospital she became the life and soul, too. The nurses used to sit beside her bed during their breaks. She was 70 years old but she was like an agony aunt to them, and they always had a laugh. Her consultant, Nigel Cox, had a reputation for being quite fierce. But mum told me she wouldn't put up with him treating her like that. They ended up as very good friends and she had complete trust in him.

Mum had been ill for 13 years, weighed five stones, was virtually blind and was in constant pain when she called me into her hospital room one night. She said she couldn't take any more, it had reached the point where everything had become too much for her. Tears were running down her face. She told me she had decided to take herself off all her tablets, except for the painkillers. I wasn't shocked. Nor did I try to dissuade her. It was mum's choice and I totally accepted it. For years she had fought to keep herself going for the sake of everyone else. Finally she was doing something for her own sake.

She said: "Nigel will look after me. He will give me something, he won't let me suffer. Then that will be it, just like having a cup of tea." But when mum mentioned it to Dr Cox, he said, "I'm afraid we don't do things like that Mrs Boyes, but obviously we will make you comfortable." The next day mum was quite cheerful, as if a weight had been lifted from her. But after that her condition got rapidly worse. My brother John and I stayed with her day and night for a week. By then she was in terrible pain. I tried to lift her hand to comfort her but that in itself was agony for her. She couldn't even stand to have the sheets resting on her skin. The slightest pressure made her flinch. And anything we said was lost in this frenzy of pain mum was experiencing. She hardly seemed able to breathe.

Dr Cox had been away for a few days and when he walked into the room I could see he was shocked at the state mum was in. He gave her an injection, I suppose of something strong to ease the pain, but it seemed to make mum worse. Then he left the room and returned with another syringe which he put into her foot. Almost immediately she calmed down. It was such a relief to be able to hold her hand again. A few minutes later she passed away.

It wasn't until after mum's funeral that I found out that the last injection was of undiluted potassium chloride and that it is fatal. The police interviewed John and me for six hours, and things snowballed from there.

It was the best part of a year later that Dr Cox was convicted of attempted murder. I was so shocked and felt incredibly sorry for him. I felt very angry that everyone was looking at it purely as a point of law and almost forgetting about the people behind the case, about what we had all been going through.

I know my mum would have been horrified to see what her death had led to, that they were doing this to Dr Cox, her friend. I was so relieved when the General Medical Council decided he could continue to practise medicine.

I think Dr Cox saw mum that day and thought: "Enough is enough." There was no pain or anything sinister involved. He even recorded the details in mum's notes. He said he thought it would have been disrespectful to her to be dishonest. It was an act of mercy, a really human thing to do.

I fully support Dr Cox's decision. Mum had hung on for a week in complete agony, John and I were cracking up to see her going through that. It sounds terrible to say it about someone you love but I was grateful to Dr Cox for giving mum that injection. Her only wish was to die in peace, and he helped her to do that.

8 Patrick Boyes was interviewed by Elizabeth Udall. He can be seen on 'Doctors in the Dock', BBC2, next Thursday