A multiple sclerosis sufferer won permission yesterday to bring a High Court challenge to clarify the law on assisted suicide.

Two judges gave Debbie Purdy leave to challenge the Director of Public Prosecutions, Sir Ken Macdonald, QC, to issue a clear policy on whether and in what circumstances people might be prosecuted if they help loved ones to die.

Lord Justice Latham, sitting with Mr Justice Nelson at the High Court in London, ruled that “without wishing to give Ms Purdy any optimism that her arguments will ultimately succeed”, she did have an arguable case that should go to a full hearing.

Ms Purdy, 45, had primary progressive MS diagnosed in 1995 and now lives in a specially adapted home in Bradford, West Yorkshire. She plans to choose her moment to die but wants to know whether her husband, the Cuban jazz violinist Omar Puente, will be prosecuted if he helps her to travel to a clinic in Belgium or Zurich, Switzerland, to commit suicide if her condition becomes unbearably painful.

Jeremy Johnson, appearing for the DPP, had said in court that Ms Purdy did not have an arguable case. But the judges ruled that the “nature of this case and its sensitivity”, which raised human rights issues, justified a full hearing.

The DPP has so far indicated that there is no specific policy for assisted suicide and that he is not in a position to grant immunity from prosecution.

Although almost 100 Britons are reported to have died at the Dignitas clinic since 1992, none of their relatives has been prosecuted for accompanying them, despite lengthy police investigations.

Ms Purdy’s application is being supported by the organisation Dignity in Dying. The case will have a full hearing in October.

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