Up before the Court of Session in Edinburgh today is a legal question: was Scottish Secretary Alister Jack’s decision to block the SNP’s gender reforms a lawful exercise of his statutory powers?

In January, Jack invoked a relatively obscure power to block the Gender Recognition Reform (GRR) Bill. The GRR Bill – the brainchild of Nicola Sturgeon and her Green coalition partner – would lower the age at which someone can change their legal sex to 16; remove the requirement for medical experts to be involved in the process; and reduce the statutory waiting period from two years to three months, plus a further three-month reflection period.

At the heart of the Bill is a principle that is still fairly new even within gender politics: self-identification. Self-identification holds that a person is whatever gender they say they are, regardless of their birth sex. If a man with male physiology declares himself a woman, then he is a woman and must be treated as such as a matter of law, custom, service provision and every other facet of life.

Naturally, the Bill was and remains controversial. Trans rights campaigners say it simplifies and renders a distressing process less humiliating. They contend that bigots are using opposition to the Bill as a cover to demean trans people. However, women’s rights activists say self-identification reduces being a woman to little more than a feeling and that the Bill would create a laxer regime that could be exploited by predators pretending to be trans to gain access to single-sex spaces and services for women.

Debates around the GRR Bill were further charged by the Court of Session ruling in For Women Scotland 2 (FWS2), in which Lady Haldane held that the definition of sex in the Equality Act 2010 is not limited to biological sex. Opponents of gender reform believe the combination of the GRR and FWS2 would collapse any meaningful differences between sex and gender in the operation of the law.

Into this maelstrom stepped Dr Michael Foran, a young, Cambridge-educated law lecturer at Glasgow University, who penned a blog arguing that the GRR Bill would alter how GB-wide equalities law functioned. Since the Scottish parliament was determined to press ahead regardless, Dr Foran suggested that the Scottish Secretary take an unprecedented step and bar the Bill from going forward for Royal Assent.

The power to make such an order is contained in Section 35 of the Scotland Act, allowing the Secretary of State to intervene where he considers a Bill before Holyrood to make ‘modifications of the law as it applies to reserved matters’ and where he has ‘reasonable grounds’ to believe the legislation would produce ‘an adverse effect on the operation of the law as it applies to reserved matters’. Within a matter of days, the Foran proposal was unofficially government policy, with No. 10 especially concerned about knock-on effects from the Scottish legislation in the rest of the country. Then, in January, the Scottish Secretary formally made the order and presented parliament with his reasons, as the Act requires.

Lady Haldane, now presiding over the judicial review of Jack’s order, will determine whether his actions accorded with the provisions of Section 35. That is a legal question but were she to rule against the UK government, the political fallout could be significant. It would be deeply embarrassing for No. 10 to lose this battle against the Scottish government, particularly if fears about the GRR’s impact on GB equalities law proved to be well-founded.

UK ministers would then be left trying to manage any fallout in England from legislation that no English MP ever got to vote on. It would represent yet another unintended consequence of Scottish devolution and a reminder that Donald Dewar’s arrogant empire-building has done far more to undermine the political cogency of the UK than it has the electoral fortunes of Scottish nationalism. Whatever the judgment of the Court of Session, the devolution settlement remains fundamentally flawed, politically injurious, and in urgent need of reform.