Next week the High Court will begin hearing two cases that raise profound ethical issues. The question in each case is whether it can ever be lawful to help another person take their own life.

This is a subject on which we might reasonably have expected parliament to give a lead. But successive governments have shied away from dealing with problems of this kind, leaving the judges to take the flak from whichever side of the right-to-life argument feels dissatisfied by the decision in each case.

The first claim is being brought by Tony Nicklinson, 58, an active, outgoing man until he was paralysed by a catastrophic stroke in 2005. The second claimant can be identified only as Martin. He had a similarly devastating stroke in 2009, when he was 43. Each man now has only very limited head movement and communicates by looking at a screen connected to a computer.

Nicklinson wants the option of ending his life at a time of his own choosing. His lawyers say he is not eligible for assisted suicide at the Dignitas centre in Switzerland because he cannot swallow a fatal dose of drugs. He has no wish to die in Switzerland anyway, even if he could get there. And he does not want to die a slow and painful death from dehydration.

Martin’s plans were less clear at the time of a preliminary High Court hearing in January. The judges thought his wife would not be at risk of prosecution if she helped him to die. However, they were told that she did not wish to play any part in hastening his death.

In April, the court decided that Martin’s case should be considered on the basis of whatever possibilities might be open to him. One option might be a trip to Switzerland. Another might be for him to refuse food and hydration, though this would need to be coupled with palliative sedation.

No court can afford to ignore the ethical implications of providing these men with the means to end their own lives. How does a judge decide whether an individual has given his or her consent? Or, indeed, is even capable of consenting? How severe does a disability have to be to justify death? Is there a ‘floodgates’ argument? A ‘slippery slope’ to euthanasia?

However, I shall confine myself to the legal issues. Nicklinson wants the court to declare that a doctor who helps someone in his position to die, with the approval of a judge, can raise the defence of necessity to a charge of murder.

That defence, he argues, has been developed by the courts over time to a point where it would be logical, just and humane to extend it to a case such as his. Prior approval by a court in each case would provide a safeguard against abuse.

In 1884, the defence of necessity was rejected by the courts in the remarkable case of R v Dudley and Stephens, immortalised a century later by Professor AWB Simpson in his book Cannibalism and the Common Law. The two shipwrecked sailors who had survived by eating the cabin boy were convicted of murder, although their death sentences were commuted to six months’ imprisonment.

The necessity defence had more success in 2001, when the courts permitted the death of one conjoined twin to save the life of the other. But, in opposing Nicklinson’s claim, the Ministry of Justice argues that the true justification for killing one of the Maltese twin sisters was self-defence, rather than necessity; Nicklinson’s lawyers disagree.

The solicitors acting in Martin’s case maintained that they risked being charged under the Suicide Act 1961 with encouraging or assisting their client’s suicide if they even advised him of his legal options. As Lord Justice Toulson indicated in January, this argument was pretty artificial.

Nicklinson’s lawyers are expected to say that doctors have a duty to ease suffering and respect a patient’s autonomy. In some circumstances, therefore, a doctor’s duty to end a patient’s life may outweigh the duty to preserve it. The government argues that necessity is no defence to a charge of assisted suicide, pointing out that recent attempts to soften the law have been rejected by parliament.

Nicklinson’s advisers also rely on article 8 of the European Convention on Human Rights – the very right of an individual to a private and family life that has so exercised the home secretary Theresa May this week. It is a right that encompasses personal autonomy and dignity.

But, as May seemed not to appreciate at the weekend, article 8(1) must always be subject to article 8(2), which allows such interference with private and family life as is necessary for the protection of the rights and freedoms of others. Government lawyers accuse Nicklinson of seeking to go behind clear rulings, from the UK courts as well as the Strasbourg judges, that restrictions on assisted suicide are a proportionate interference with article 8(1) and therefore justified under article 8(2).

Again, Nicklinson’s lawyers disagree, seeking a declaration of incompatibility that could trigger fast-track legislation.

The reality is that this case is likely to be anything but fast. If, as expected, it goes via the Court of Appeal to the Supreme Court, we may not get a final ruling before 2014. But that is no bad thing. Neither Nicklinson nor Martin seem to be in any great hurry to end their lives. Reaching the right conclusion is, for once, vital.