On a steamy night in Singapore 13 years ago, Debbie Purdy went to hear a Cuban band play at the island’s World Music Club. She had been feeling uncharacteristically low, but her mood picked up when she caught the eye of the band’s handsome violinist, Omar Puente. “I thought he looked like a mafioso, with his dark hair and thin moustache,” she says.

Over a drink, she and Puente got talking, in a mixture of bad Spanish on her part and broken English on his. They went on a few dates. Then Purdy flew back to England for what she thought would be a one-off appointment with a neurologist recommended by her GP.

The feeling of sluggishness and low spirits that she had put down to losing both her parents in quick succession and then spending a dreary, cold autumn in England – for which she had prescribed herself a prolonged break in Singapore – turned out to be the first signs of degenerative, devastating multiple sclerosis.

“Instantly, I knew my life was going to change,” she says. “I’d spent 10 years travelling around the world, skiing, waterskiing, diving, para-chuting and making a living moving from one job to another. I didn’t know what my life would be now, but I knew that couldn’t continue.

“I thought I’d return to Singapore just to pick up my stuff and I called Omar to let him know what had happened – I had to speak to the Spanish embassy first to find out how to say multiple sclerosis in Spanish. I wasn’t sure whether he’d understood what I was trying to tell him.

“I assumed that was the end of things, but when I got off the plane at Singapore, there he was, waiting. I’d only told him the day I was coming back, not the time. He’d played with the band the night before, had breakfast with some friends at 2am then headed out to the airport and met every plane.”

They married ten years ago and Puente, now an established session musician, will be at Purdy’s side again this Thursday, at the High Court in London. She won the right to a judicial review of the law on assisted suicide in June – but admits to feeling “terrified” at the prospect of going back to court.

Her condition has deteriorated to the point where she is no longer able to walk, the least effort makes her exhausted and her sight and hearing have begun to fail. Despite all that, she has a wonderfully cheery smile and insists that she “loves life”. Yet she knows she is inexorably heading towards the point where she will find her life intolerable.

When that time comes, she wants to be able to end her life by travelling to the Dignitas clinic in Switzerland. If Puente helps her do it, he faces up to 14 years in prison. “I really want to have a legacy,” she says, “and I don’t want my legacy to be that my husband gets locked up.”

The law on assisted suicide as it stands is vague, perhaps deliberately so. The 1961 Suicide Act makes it illegal to “aid, abet, counsel or procure the suicide of another”. How that law is interpreted is a lottery: two years ago, Paul Weber, referred to in court as a “devoted son” who had cared for his mother for 18 years, was jailed for 12 months for strangling her after she took an overdose. He also took an overdose and intended to die with her.

Others who have publicly admitted to helping loved ones to die have been questioned or held overnight by the police – or have continued with their lives without being in any way held to account. The Turner family – siblings Edward, Sophie and Jessica – who told their story in these pages two years ago after accompanying their mother, Dr Anne Turner, who was suffering from progressive supranuclear palsy, on a last journey to die in Switzerland, received an embarrassed phone call from the police a few days after the article was published.

“Some religious opponents of assisted suicide had put pressure on them to prosecute us,” says Edward Turner. “The detective said he’d been told that if you push a wheelchair, that isn’t aiding and abetting – but if you administer drugs, that is. So we were lucky, as we’d only travelled with our mother, but to me the crime would have been to allow her to do that journey alone.”

Purdy, 45, who describes herself as “a planner and preparer”, isn’t content to leave her husband at the mercy of the police, however sympathetic they might be. Despite their years together, his command of English is not good: he might easily be tripped up in a hostile police interview. “If they wanted to make an example of someone, they would be more likely to go for him than some 78-year-old war veteran,” she says.

And, besides, he would be distraught: “He wouldn’t have me to protect him. He would be grieving for his wife; he’d need to deal with what had happened . . . it doesn’t bear thinking about that he would be further hurt. He says he would be prepared to go to jail for me, no question, but I love him and, however remote the chance, I won’t let that happen.”

Last week, Baroness Warnock created a stir by suggesting that the elderly or infirm should be allowed to die if they felt they were becoming a burden to their families. “If you are demented, you are wasting people’s lives, your family’s lives, and you are wasting the resources of the National Health Service,” she said. Mary Warnock’s view of the world supposes that it is the disabled partner who is the dependant, but Purdy and Puente’s relationship seems more complex.

When she returned to Singapore after her diagnosis, he persuaded her to move into the house where his band were living. She spent the next two years booking their gigs, arranging visas and organising their travel, before moving home to Brad-ford, where she married Puente in 1998. “I looked after the band and the band looked after me,” she says. “It didn’t bother them if I couldn’t walk too well at times. Coming from a poor place like Cuba, they’d seen people struggling in all sorts of ways; that’s just life. I think that’s why Omar’s stayed around, when an English guy might have walked.

“Omar’s never felt sorry for me. Early on, he said to me, ‘I can either cry with you or laugh at you – which do you want?’ and we’ve laughed and laughed. And he plays music that’s electric and vibrant, makes me glad to be alive.”

As if on cue, Puente calls. He’s got a stomach upset. “Drink some milk then,” Purdy advises. “If they’re on tour in Germany, he rings me to ask what kind of beer he should drink, too,” she says, laughing. “See? We’re equals.”

She says she’s not ready to die, but if she does not get the clarification she seeks in court this week, she may have to take her life sooner rather than later, while she is still able to do everything necessary without help – which sounds pretty close to emotional grandstanding.

“Nothing of the sort,” she insists. “If a man was dehydrating in the desert and said, ‘Give me some water, or I will die’, that’s not emotional blackmail – that’s just a fact.”

What scares her most about the prospect of this week’s hearing is not getting a conclusive answer and having to take the case on to the House of Lords. Every week she feels her condition slightly worsens.

“This is my life, not some theoretical question to be kicked around as a legal or political football. The law says ‘aid, abet or counsel’ – does that mean that by talking to me about what I might want to do, Omar has already done something illegal? That’s all I want to know: just where does he cross the line?”

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