Margaret John at her home in York. She says that ‘when you have cancer, you can’t control it – it controls you’ / Lorne Campbell / Guzelian

When Margaret John learned that her cancer was spreading again, she asked a doctor for advice on suicide and was refused. Now she has taken her case the Supreme Court

Margaret John can vividly remember the day she asked her GP for advice on the best way to kill herself. What had begun as ovarian cancer was spreading throughout her body, and Ms John, who is 73, wanted to know which drug might offer the most peaceful way out.

“I asked my GP whether there was anything currently on prescription that would do the job and he said: ‘I’ll be honest with you, I don’t kill people’,” she recalls. Still hoping to find a solution, she turned to the web. “I wasn’t happy with what I found on Google. I only shop online at places I trust, like John Lewis. One of the irritations with this is, what if it doesn’t work? You can’t sue them because you haven’t died. You can’t get your money back.”

Ms John, a retired geography teacher who lives in York, wants the right to expert advice on finding a humane way of ending her life once the terminal cancer becomes unbearable. Her testimony will be considered in the Supreme Court this week. Beginning today, judges will attempt to clarify the issue of whether doctors can help someone with a serious illness who wants to die.

The court will deliberate over four days, using fresh testimony from Ms John and another terminally ill man – Roch Maher, a 52-year-old who was diagnosed with motor neurone disease in 2009. But the hearing will centre around the three previously failed cases of the late Tony Nicklinson, who suffered from locked-in syndrome and died after refusing food; stroke sufferer Paul Lamb, and a man named as ‘Martin’ with motor neurone disease. All of them wanted help to die.

Ms John’s travails with cancer over the past four years will be familiar to many with an experience of the disease. She was diagnosed with stage three ovarian cancer in 2009, which meant cancerous cells had occupied “the whole of the abdomen”. Her first round of chemotherapy began within weeks. Two months later she had her uterus and ovaries removed, as well as the lining of her abdomen.

Around a year later, further growths were discovered and in December 2011 more chemo was followed by “radical surgery,” leaving her reliant on a colostomy bag, which, as she dryly observes, “isn’t the accessory of choice”.

Beset by so much ill health, many people would lose the will to go on, but Ms John wanted to live. “Within a year I was feeling fine and enjoying life. I’d even got used to the colostomy,” she says.

Then in October last year she discovered a small lump in her breast. The radiotherapy she then received was so powerful that it masked the symptoms of the return of ovarian cancer. Now her treatment options are limited. She is undergoing light chemotherapy but is so riddled with the disease that she knows there is little time left.

Speaking animatedly in her front room, her only concession to pain is a brief pause mid-conversation to take two paracetamol. She had chemotherapy two days ago but she is energetic, insisting on running off to bring mugs of fresh coffee. She is not beyond a touch of black humour. Describing the effect of flatulence – a symptom of her cancer – on a colostomy bag, she says: “You can’t hide it. The bag blows up and you’re walking around with a balloon on your front.”

The combination of these indignities and what she refers to stoically as “discomfort” would be enough for some to long for the end. But Ms John, who keeps busy doing voluntary work for cancer charities, makes clear she’s not ready to go yet. She just wants the right to expert advice. “I’m not at all depressed or miserable. If I could get the advice on what to do [to die] I would leave it quite late.” She’s also signed up to help the Care Quality Commission with inspections and hopes one day to turn her cancer diary into a book.

So how did someone with such a zest for life become so involved in campaigning for help with its end? She puts it simply: “I want to live right up until the last minute and not just exist. There’s a difference between living and existing.”

Ms John was a member of the campaign group Dignity in Dying long before she was diagnosed, after seeing streams of friends and family suffer needlessly drawn out, painful deaths. “I have a living will and my children have known for quite a long time that I have quite strict rules of do not resuscitate in certain circumstances,” she says.

The rules are not indiscriminate though. When she was about to go under the knife in a recent operation, the anaesthetist leaned over and said, “Oh, I see you’re a Do Not Resuscitate”. She panicked: “I said, wait! Make sure you read it please, because it’s not in all circumstances and I’m definitely not ready to go yet!”

When she is ready to go she faces a dilemma. She is divorced and is “pretty sure” her two grown-up children would not want to help her die. She also knows the Dignitas clinic in Switzerland, where assisted suicide is legal, is not an option. “Dignitas is so clinical and industrial”, she says. “They do their best to make it human, but it’s a Portakabin on an industrial estate. And it’s also too expensive.”

Her wish, when it all gets too much, is to die at home. “I don’t want to die abroad, I want to go out at home, with all my things and with Verdi playing very loud, or possibly one of my jazz records.”

She believes that the most humane thing would be if it doctors were allowed to advise on the least painful way to go. “I feel very strongly that the right to be able to ask for advice is what is most lacking. I can’t ask the people who are best placed to help me because I would put them in an invidious situation.”

“I’m a control freak and I’ve got to be in charge, but when you have cancer you can’t control it – it controls you. I want to be able to discuss with someone who can say ‘I wouldn’t take that, but if you really have to do this then try that’.”

Gradually her small pleasures are being taken away. She has lost sensation in her hands and feet and cannot hold a book any more. She cuts her fingers doing needlework.

“I’m not saying that I’d necessarily commit suicide,” Ms John says. “I’d just like to know what I can do if the alternatives are extreme pain or taking a chemical cosh and being unable to recognise people. We shouldn’t make human beings go through what we wouldn’t put animals through.”

The fight to die: Timeline

2002 A man with terminal cancer is the first UK citizen to travel to the Dignitas clinic in Switzerland to end his life.

2003 Lord Joffe makes first of four failed bids to pass a Bill legalising assisted suicide.

2008 Debbie Purdy, who has multiple sclerosis, tries to establish if her husband could be prosecuted for helping her to die. The High Court refuses to say he would not be.

2010 New guidelines put greater emphasis on motivation; meaning cases against those acting with compassion are unlikely to be pursued.

2012 The High Court hears Tony Nicklinson’s bid to let a doctor end his life without fear of prosecution. He loses – and dies shortly afterwards.

2013 A Nicklinson appeal is lost – but it is being looked at again this week.