Debbie Purdy loves life. The 41-year-old from Bradford describes herself as an adrenaline junkie. In her time Purdy has jumped out of planes, climbed mountains, trekked through jungles and scuba-dived. These days her biggest buzz comes from walking unaided.

Purdy has suffered from chronic and progressive multiple sclerosis for a decade. 'I don't have relapses or remissions, I just get steadily worse,' she says breezily.

Recently she started dropping things, something that has made her think about her life - and her death. 'At some point I know I will not be able to handle drugs and take an overdose. Before that happens, I've got to make a decision: should I end my life now? When the pain becomes unbearable and I've lost my dexterity completely, I won't be able to do it myself.'

Purdy has every intention - and gives every indication - of being around for many years to come. But it is a question she urgently needs to address now so that she can concentrate on enjoying the rest of her life. 'I couldn't ask my husband to help me because there is the possibility that he would be jailed for it. It's going to be hard enough for him losing his wife - I couldn't ask him to risk being prosecuted.'

Assisting suicides carries a maximum 14-year sentence in Britain, one of the few European countries where it is still a crime. Purdy, like her 55,000 fellow members of the Voluntary Euthanasia Society, believes this is wrong. 'The only thing that will improve the quality of my life now is a change in the law, so I don't have to be thinking about what I'm going to have to do by myself. If that no longer becomes the biggest question in my life, then I can start thinking about overcoming the symptoms I cope with.'

She considered going to Holland, where euthanasia for the terminally ill has been legalised. But patients need to have been registered with a Dutch doctor for two years before they qualify for medical assistance that would bring their lives to an end.

Purdy's hopes for a law change look slim, at least for now. 'People want to bury their heads in the sand on this issue. The other day I heard Linford Christie say "oh they could find a cure". That's just grabbing at straws. That's denial.'

She says she understands people's objections to euthanasia. 'In no way do I want to make it compulsory for someone to have to participate in assisted dying but, on the other hand, I don't have a moral or religious problem with it. It would improve my life and I don't want others to disrespect my opinion, either.

'My doctor doesn't feel comfortable with euthanasia. Fair enough. But I should be able to find a doctor who does feel comfortable with it. It's the same with abortion. My doctor feels uncomfortable with abortion, but when someone is seeking an abortion they're allowed to ask for a doctor who is comfortable with it. We're just asking for the same rights. I don't want to plan my death. I want to enjoy my life.'

It is a wish that is echoed by a growing number of people in the UK who want the right to make the decision about when and how their lives should end.

Improvements in healthcare have created an ageing society, but with the consequence that more and more people are spending the last years of their lives in pain from crippling diseases.

The government's solution has been to promise more money for palliative care. But pro-euthanasia groups believe this does not go far enough. They have criticised successive UK governments for failing to follow their European counterparts and investigate the argument for clarifying the law on assisted dying.

The government's failure to do so is unsurprising. Death is rarely a vote winner and politicians are wary about antagonising the pro-life lobby, which has produced some powerful arguments against euthanasia.

The Christian Medical Fellowship, for example, makes a persuasive case that people with a terminal illness are vulnerable because they worry about the burden they place on their family. Legalising assisted dying could increase this pressure, the CMF believes.

But the government's reluctance to discuss euthanasia has confused an already complex area of law. The word has come to be a 'catch-all' term encompassing everything from mercy killings to doctors administering lethal drug doses to patients in a coma.

'The problem has been to get the debate into the public forum, one that will allow people to be honest about their experiences,' acknowledges Deborah Annetts, chief executive of the Voluntary Euthanasia Society.

Amid the lacuna, people have started to take the law into their own hands. The Switzerland-based group, Dignitas, claims to have helped 22 Britons with terminal illnesses die abroad. Hardly a month goes by now without a pensioner confessing to killing a partner who was in agonising pain.

The CMF rejects the claim that euthanasia is a solution to patients' distress. 'Meticulous research in palliative medicine has in recent years shown that virtually all unpleasant symptoms experienced in the process of terminal illness can be either relieved or substantially alleviated by techniques already available,' it suggests.

But this argument is rejected by many in the medical professions. Just over half of nurses questioned in 2003 said the law should be amended to allow health professionals to help terminally ill people die.

In 1996, 54 per cent of 1,000 doctors questioned in a survey said they were in favour of legalising physician-assisted suicide in specific circumstances. The same survey found 3 per cent of GPs had helped terminally ill patients to die. That number is likely to have increased after several recent high-profile campaigns. The case of Diane Pretty, the woman with motor neurone disease who lost her high court fight to have her husband help end her life, attracted widespread media interest.

Now, in the latest assault on the pro-life lobby, crossbench peer Lord Joffe is attempting to steer a private member's bill legalising assisted dying through the House of Lords. Under Joffe's proposals voluntary euthanasia would be made available to patients who have less than six months to live and who are in 'unbearable pain'. Their decision to hasten an end to their life would be accepted only after they had undergone psychiatric and medical examinations and had been given a 'cooling-off' period to allow them to change their mind. Tory peers vehemently oppose the bill which had attracted 100,000 submissions when its consultation process was completed earlier this month.

Few think Joffe's bill will make it to law. But it may come to be seen as an important step towards legalised euthanasia in Britain.

Evan Harris, Liberal Democrat MP for Oxford West and Abingdon, gave evidence to the committee in which he recalled seeing terminally ill patients pumped full of morphine to speed their demise when he was working as a doctor. Harris believes a change in the law is necessary to regulate a practice that clearly exists but remains hidden behind closed doors.

'Doctors are always reluctant to see any change in the doctor-patient relationship, but I don't think they would oppose it if it became law. They accept it's a matter for society,' Harris says.

Annetts believes the combination of an ageing population and an increasingly secular society will become a catalyst for change.

'Ultimately the government will have to engage with this issue. The great thing about the euthanasia debate is we all have a view. We are all going to die.'