The moral case for the reform of Northern Ireland’s harsh abortion laws, which forbid terminations even in the case of rape or fatal foetal abnormalities, has long been clear. But the sweeping victory for reform in the Irish abortion referendum last month made it starker than ever. The logical case is obvious: the restrictions do not prevent but displace abortions, with women travelling across the Irish Sea to end their pregnancies. The political case is equally evident: poll after poll has shown that voters in Northern Ireland believe the law must change. Now the supreme court has laid out the legal case.

By a narrow majority, the judges of the UK’s highest court ruled that it had no jurisdiction to consider the legal challenge brought by the Northern Ireland Human Rights Commission because there was no actual or potential victim involved. (A Belfast woman now plans to challenge the law in her home city’s high court.) They could have stopped there. Instead, the majority went on to state that the current law is incompatible with the right to respect private and family life, guaranteed by the European convention on human rights, in prohibiting abortion in cases of rape, incest and fatal foetal abnormality. Two of the seven concluded that it was also incompatible with the right not to be subjected to inhuman or degrading treatment. Technically speaking, this is not a declaration of incompatibility. But its effect is to make such a declaration unnecessary.

The judgment should concentrate the minds of both Theresa May and Arlene Foster. To simply repeat that abortion is a devolved issue is inadequate when it is the UK government that is responsible for compliance on rights. The DUP leader, whose party vehemently opposes abortion reform, accuses others of seeking to circumvent the role of the Northern Ireland assembly. This is utterly disingenuous when the collapse of power-sharing means that the assembly has not sat for almost a year and a half.

Central government should be cautious of overriding devolved ones. Such actions can foster local anger and have perilous consequences. But Mrs May has other matters in mind too. She acknowledged in a private meeting of Conservative MPs that she is concerned about the issue’s potential to unsettle crucial Brexit votes. She argued that it may also hamper efforts to restore power-sharing. Most surmise she is more concerned by the precariousness of her own government, propped up by the DUP. But Mrs Foster also has much to lose should their pact collapse, unless she is happy to risk a Jeremy Corbyn government.

Mrs May should call her bluff. The restoration of power-sharing is long overdue: Northern Ireland’s politicians should get on with it, and then change the abortion law. For the case for change is uncontestable and the mood in Westminster is toughening. Penny Mordaunt, minister for women and equalities, tweeted of this week’s debate on the law: “Message from NI Secretary of State: NI should take that responsibility. Message from the House of Commons: if you don’t, we will.”