The Scottish and UK governments are heading to court over a plan to change the law in Scotland to make it easier for people to change their legal gender. A legal expert explains what the dispute is about and why it has serious constitutional implications.

What is the law at the centre of this argument?

The Scottish parliament passed the gender recognition reform (Scotland) bill in December 2022, amending the law in Scotland to make it easier for a person to change their legal sex. The bill makes it possible to obtain a gender recognition certificate without a medical diagnosis and reduces the time period that someone has to live with their acquired gender before qualifying for a certificate. It also makes it possible for 16- and 17-year-olds to obtain a gender recognition certificate.

What action has the UK government taken in response to this law?

On January 17, the UK government made an order under section 35 of the Scotland Act 1998.

This blocks the Scottish bill from receiving royal assent from the King, which is needed for it to become law. It does this by directing the Presiding Office of the Scottish Parliament (the Scottish equivalent of the Speaker of the House of Commons) to withhold the bill from receiving royal assent.

What is the Scotland Act?

Devolution is the process whereby Westminster gives or "devolves" legislative and executive powers to the constituent nations of the UK so that they may have greater control in governing their own affairs. Scotland, Wales and Northern Ireland have some form of devolution, but England does not.

The Scotland Act 1998, enacted by the Westminster parliament, forms the basis of Scotland's devolved settlement. It created both the Scottish parliament and the Scottish government. The legislative competence of the Scottish parliament is, however, not without limit. It cannot pass laws on "reserved matters" – those issues which the Scotland Act states only the UK parliament can legislate on. By implication, anything not identified as a reserved matter is classified as a "devolved matter" and thus within the competence of the Scottish parliament to legislate on.

The UK government has the power under the Scotland Act to veto a bill by issuing a section 35 order.

What is a section 35 order?

A section 35 order can only be made under limited circumstances. In this instance, the UK government has made the order under section 35(1)(b) of the Scotland Act. This concerns bills which the UK government believes "make modifications of the law as it applies to reserved matters" and which the UK government has "reasonable grounds to believe would have an adverse effect on the operation of the law as it applies to reserved matters". The UK government is required to set out its reasons for making this argument.

In its reasoning the UK government appears to accept that the Scottish parliament has the power to amend the Gender Recognition Act 2004 as it applies to Scotland. Its main objection to the Scottish bill is that the specific modifications it proposes affect a reserved matter – equal opportunities laws as set out in the 2010 Equality Act. While gender reassignment is a devolved matter for Scotland, equal opportunities is a reserved matter, and therefore something that can only be changed at Westminster.

What is the UK government's argument against Scotland's changes?

According to the UK government, the bill could exacerbate (mostly existing) issues involving clubs and associations that have rules relating to gender, the public sector equality duty, equal pay and the application of exceptions for both sex and gender reassignment.

The UK government also argues that the Scottish bill creates a new problem for schools because single-sex schools would be at greater risk of direct gender reassignment discrimination should they refuse admission to someone with a gender recognition certificate. This may have a further administrative impact and safeguarding risk for schools in England, especially near the Scottish border, which take in both Scottish and English pupils.

The UK government also says it is concerned that changing the way gender recognition certificates are granted in Scotland would mean it would be implementing a different system to the rest of the UK. As a result, a person could have one legal sex in Scotland but a different one in the rest of the UK. According to the UK government, this is likely to have adverse consequences on other reserved matters, such as the administration and management of tax, benefits and state pensions.

By making it easier to change legal sex in Scotland without a medical diagnosis and without evidence of living in their acquired gender for two years, the UK government also contends that the proposed Scottish system is more open to abuse, thus potentially making, for instance, sex-segregated spaces more unsafe for women and girls and therefore discouraging them from using them.

What will happen next?

First minister Nicola Sturgeon has indicated that the Scottish government will seek a judicial review of the decision by the UK government to exercise its section 35 veto power in this case.

Judicial review is a legal action focused on the lawfulness of a governmental decision, not its merits. It is therefore likely that any judicial review will turn on the extent to which the law as it applies to reserved matters would be modified by the Scottish bill and whether there are "reasonable grounds" to believe that there would be adverse effects.

Should the Scottish government succeed in its case, it's likely that the section 35 order would be struck down and the bill would receive royal assent and become law. Should it fail, it could reintroduce an amended bill into the Scottish parliament addressing the concerns of the UK government. However, given the UK government's reasons for objecting to the bill, it's hard to imagine how any amendments could achieve this in full.

The judicial review action will start at the court of session in Edinburgh and will then likely be appealed to the UK supreme court.

Why is this situation being viewed as a potential constitutional crisis?

This is the first time section 35 has ever been used in the almost 25 years since Scottish devolution.

Although the veto can only be used in limited circumstances, thus explaining in part why it has never been used until now, the constitutional implications of the decision cannot be overstated. In effect, a UK minister has vetoed a bill on a devolved matter enacted by a two-thirds majority of a democratically elected parliament. Regardless of one's views on the merits of the Scottish bill, this has significant political and constitutional ramifications, especially during a protracted period of increased tension between the Scottish and UK governments.

The dispute may further strengthen calls to hold a second independence referendum in the near future, and may be a crucial factor in any de facto referendum on Scottish Independence at the next general election should the Scottish government proceed with this plan.

Robert Taylor is Senior Lecturer at the School of Law at the University of Aberdeen. This article is republished from The Conversation under a Creative Commons license.