A woman suffering from primary progressive multiple sclerosis took her legal battle to clarify the law on assisted suicide to the Court of Appeal today.

Debbie Purdy, 45, wants to know if her husband, the Cuban violinist Omar Puente, will be prosecuted if he helps her to travel abroad to die in Switzerland, where the practice is legal.

She is seeking guidelines from the Director of Public Prosecutions as to his policy on the circumstances in which a person would be liable to prosecution for helping another commit suicide.

In England and Wales, aiding and abetting suicide is a criminal offence punishable by up to 14 years in prison.

Ms Purdy, 45, from Undercliffe, Bradford, West Yorkshire, wants to know whether her husband would be liable if, for instance, he helped her to buy train tickets or accompanied her abroad to take her life.

Without any such assurance or clarification, she will be obliged to end her life while able to make all the arrangements herself, which would be sooner than she otherwise might do.

Ms Purdy said that she was "disappointed and shocked" when the High Court recently rejected her bid to obtain legal certainty and peace of mind.

Today Lord Pannick QC, appearing for Ms Purdy, argued the High Court judges had erred in law.

The appeal is being heard by the Lord Chief Justice, Lord Judge, sitting with Lords Justices Lloyd and Ward, over two days.

As Ms Purdy and her husband listened in court, Lord Pannick argued that the Director of Public Prosecutions, Keir Starmer QC, should be required to issue specific policy guidelines. Such guidelines already exist for crimes of domestic violence, bad driving and football-related offences.

Lord Pannick told the judges that the appeal concerned "whether the Director has a legal duty to adopt and publish a policy as to the criteria to be applied by him, and by Crown prosecutors on his behalf, in deciding whether to bring a prosecution for aiding and abetting suicide, contrary to the Suicide Act".

Lack of proper guidance infringed Ms Purdy's Article 8 right to private and family life under the European Convention on Human Rights, he argued.

In October, Lord Justice Scott Baker and Mr Justice Aikens, sitting at London's High Court, expressed sympathy for the couple, and others in a similar position. But they ruled that the Code of Practice for Crown Prosecutors already issued by the DPP, coupled with the general safeguards of administrative law, satisfied human rights convention standards and met the need for "clarity and foreseeability".

In addition, the DPP, Keir Starmer, QC, recently issued a full statement of reasons when he decided not to prosecute the parents of Daniel James, a paralysed rugby player who went to Switzerland to take his own life. He has indicated that this comes as close to a statement of policy as could make.

Ms Purdy, whose legal action is supported by Dignity in Dying — formerly the Voluntary Euthanasia Society — was diagnosed with primary progressive MS in 1995 and has been a wheelchair user since 2001.

Ms Purdy says she wants to "live forever". However, she is a member of Dignitas, the Swiss organisation that operates specialist euthanasia clinics.

Now gradually losing strength in her upper body, she plans to travel to Switzerland to end her life if her condition becomes unbearable.

Her lawyers argue that, unless the law is clarified, her life will be shortened as she will have to travel earlier because her husband will not be able to assist her without risking jail.

Dignitas opened in 1998 and has so far helped more than 100 british citizens to end their lives. It currently has upward of 694 UK members.

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