A terminally ill woman who fears that her husband will be jailed for helping her die painlessly will go to the High Court next month in a landmark challenge to the law on assisted suicide.

Debbie Purdy, 45, says she wants to end her life with her Cuban-born husband by her side in a Swiss clinic which helps patients die at a time of their own choosing. But under British law, anyone who assists another person commit suicide – for example, by helping them travel to a suicide clinic – is at risk of criminal prosecution and up to 14 years' imprisonment.

Ms Purdy, and hundreds of terminally ill people like her, believe the law is depriving her of the comfort and solace of the man she loves at the time when she needs him the most. If the law can't be changed, then she asks for the right to know how the law is enforced in these kind of cases; she wishes to die knowing her husband will not be prosecuted.

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Ms Purdy first met Omar Puente, 46, in a Singapore bar in 1995, just as she was first experiencing the early symptoms of a progressive form of multiple sclerosis. He was playing violin with a Cuban salsa band and she had been assigned to write a magazine review of the performance. "I think he was told by the band leader to be nice to me," she told The Independent yesterday.

"We soon started dating and a few weeks later I returned to England, when the family doctor diagnosed me as suffering from MS. We have been together ever since. Omar jokes that he has only ever known the MS Debbie, not the healthy Debbie."

The High Court judicial review to force the Director of Public Prosecutions to declare his policy on prosecuting assisted suicide cases begins on 2 October. Ms Purdy will be represented by David Pannick QC, a leading expert in public law and human rights.

It has just emerged that 650 British citizens have now signed up with Dignitas, the Zurich clinic which helps terminally ill patients end their lives in comfort and dignity abroad.

Many British Dignitas members wish to know whether or not their relatives will be liable for prosecution under the Suicide Act 1961 if they accompany them to the clinic or assist in any way with their travel arrangements.

The uncertainty of not knowing what risks her husband faces under British law has caused Ms Purdy great anxiety. "I can't let him travel with me to Switzerland because that might be construed as assisting me in my death," she said. "He says he is prepared to face jail if it means he could do something to stop making my life unbearable."

As a younger woman, Ms Purdy enjoyed travelling the world working as a dancer, waitress and writer. "I learnt to ski and waterski and I loved throwing myself out of aeroplanes," she said. Today she is confined to a wheelchair and has trouble taking a sip of water: "I'm much more frightened of choking to death or being in extreme pain than dying early," she said.

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Ms Purdy first knew something was wrong when she went dancing with friends at a Yorkshire nightclub. "It was like dancing in sneakers with chewing gum on. My feet were moving very slowly and I didn't know why... At first the doctors said that it was depression after the death of my mother."

By the time Ms Purdy returned to Singapore to join Mr Puente, she had sought a second doctor's opinion which confirmed her worst fears. "I rang the Spanish embassy to ask what the Spanish for MS was so that I could telephone Omar and tell him what I had," she said. "I didn't know what he would think, how could I? But when I arrived at the airport, he was waiting for me."

Mr Puente asked her to move in with the band and for the next two years she travelled all over Asia with them. "Whenever anyone booked us, the band always said I was part of the deal."

But Ms Purdy's health was rapidly deteriorating and she decided to return home to Bradford. "I asked Omar if he would give England a try. He came for a month and got to know a Bradford salsa band. Although he finds the weather too cold and wet, he likes the people very much. Omar decided to stay and in 1998 we were married."

The couple are still together today. When Mr Puente's mother died, his wife was there to help him through it. Now Ms Purdy, the youngest of five siblings, says the time is fast approaching when she will have to choose the way she ends her own life.

In the past six years, nearly 100 British people have chosen to end their lives with Dignitas. Now, 40 relatives of former Dignitas patients have submitted witness statements to the High Court in support of Ms Purdy's case.

The charity Dignity in Dying, which campaigns for a law that will permit the assisted death of terminally ill adults at a time of their choosing, is also backing the High Court action. Its chief executive, Sarah Wootton, says the rate of inquiries from people wishing to follow the Dignitas route has increased over the past year. In the past fortnight she said she had been contacted by two men, one suffering from advanced leukaemia, who both wanted advice. She described them both as in the advanced stages of arranging their own deaths.

Although nobody has been prosecuted for providing assistance to a relative who used Dignitas, Ms Purdy believes her husband faces a great risk. "He is black, foreign and has very little money – that's not a great thing to be today," she said. "After I have gone I don't want him to fall foul of the law for being the wrong colour, from the wrong country and from the wrong class."

Assisted suicide

Netherlands

In 2002 the Dutch government became the first to introduce an assisted dying law. The courts permit about 3,500 cases a year. All patients must have an incurable condition.

Switzerland

The only country to permit non-Swiss residents to take advantage of its assisted dying code. The law makes clear that a person can assist another's suicide providing they act out of the highest sense of morality. But voluntary euthanasia is still forbidden in Switzerland.

Belgium

The Belgium Act on Euthanasia was passed in May 2002. Patients have to be in a "futile medical condition of constant and unbearable physical or mental suffering that cannot be alleviated".

Luxembourg

The latest country to bring in an assisted dying bill, which is expected to come into force this year. The law was passed by a majority of just four.

Oregon

In 2006 the US Supreme Court upheld a law allowing doctors in Oregon to help terminally ill patients to die. Justices voted by 6 to 3 to back the law.