When does a “woman” include a biological male? And who gets to decide – Parliament or the courts?
This seemingly simple question was at the heart of last week’s UK Supreme Court decision. The case offers a striking contrast to our own Supreme Court’s approach to statutory interpretation.
For Women Scotland v Scottish Ministers [2025] UKSC 16 involved a court challenge to the Gender Representation on Public Boards (Scotland) Act 2018. This Act set a target that 50% of non-executive members of public boards should be women. It defined “woman” to include transgender women – specifically, a person who is “living as a woman and proposing to undergo, undergoing, or having undergone a process… for the purpose of becoming female.”
The challenge centred on whether the Scottish Parliament had exceeded its legislative powers. Under the UK’s devolution settlement, the Scottish Parliament cannot legislate on “equal opportunities.” Instead, this issue is a matter reserved for the UK Parliament. For Women Scotland argued that by defining “woman” to include some biological males, the Scottish Parliament had impermissibly legislated on equal opportunities.
The UK Supreme Court unanimously sided with the challengers, finding that the Scottish Parliament had indeed exceeded its legislative competence. The Court held that the definition of “woman” in the Act modified the protected characteristic of sex in the Equality Act 2010 – a matter reserved exclusively to the UK Parliament.
Restrained approach
What makes this decision particularly instructive is the UK Supreme Court’s disciplined approach to statutory interpretation. The Court emphasised that statutory interpretation requires an “objective assessment’ of Parliament’s intended meaning” (para 9), that courts must act “within the permissible bounds of interpretation” to give effect to Parliament’s purpose (para 10), and that statutes should be understandable by citizens who must able to “rely on the words enacted by Parliament” (para 10).
The Court carefully examined the Equality Act 2010 and interpreted it according to Parliament’s intent at the time of enactment. It confirmed that “the words ‘sex’, ‘woman’, and ‘man’ in sections 11 and 212(1) mean (and were always intended to mean) biological sex, biological woman and biological man” (para 264). The Court explicitly clarified that while “sex” and “gender” were historically used interchangeably, the Equality Act distinctly referred to biological sex.
The Court explained further that while section 9(1) of the Gender Recognition Act 2004 generally allows those with a Gender Recognition Certificate to be treated legally as their acquired gender, that treatment is explicitly subject to contrary provisions enacted by Parliament (paras 24, 157).
Rather than attempting to update or reimagine the meaning of “sex” in the Equality Act based on contemporary social values, the Court gave effect to Parliament’s original intent when enacting the legislation.
This rigorous approach ensured citizens can reliably regulate their conduct based on what they read in an Act – a fundamental requirement of the rule of law.
Comparing approaches
The restrained approach of the UK Supreme Court stands in stark contrast to the loose approach of our Supreme Court. As I have written elsewhere, our highest Court has shown an increasing willingness to stretch or ignore clear statutory language when it conflicts with judges’ perceptions of contemporary values.
In Fitzgerald v R [2021] NZSC 131, our Supreme Court effectively rewrote the “three strikes” provision by inserting an exception for disproportionate punishment that Parliament deliberately chose not to include.
Similarly, in Attorney-General v Family First New Zealand [2022] NZSC 80, the Court denied charitable status to an organisation advocating for traditional family values. Despite the Charities Act 2005 explicitly requiring that charitable entities apply income to charitable “purposes” in section 13(1), the Court effectively rewrote the statute by requiring Family First’s “activities” themselves to be charitable. The outcome denied a conservative group charitable status. AN Australian commentator described this as “court sanctioned social engineering.”
A more recent example of our Supreme Court’s ‘liberal’ approach to statutory interpretation is its Edwards decision on the Marine and Coastal Area Act (Whakatōhea Kotahitanga Waka (Edwards) v Ngāti Ira O Waioweka [2024] NZSC 164). There, the Court effectively rewrote Parliament’s structured legislative framework by inserting tikanga considerations, which Parliament had chosen not to include.
This tendency toward judicial rewriting of statutes reflects a broader, concerning view about statutory interpretation.
Misguided ambulatory approach
Some commentators – including one of our own Supreme Court judges, writing extra-judicially – have suggested section 11 of our Legislation Act 2019 entitles the courts here to take a more expansive approach to statutory interpretation than would otherwise be permissible. Section 11 states that “legislation applies to circumstances as they arise,” and it has no equivalent in the UK’s Interpretation Act 1978.
In a 2018 essay, “Mired in the past or making the future?” Justice Glazebrook contended that section 11’s requirement to apply legislation to “circumstances as they arise” authorises courts to interpret statutes in light of evolving societal attitudes and values –effectively endorsing an ‘ambulatory’ approach to statutory interpretation. On this basis, one might wonder whether Justice Glazebrook would have adopted a more expansive approach than the UK Supreme Court had the For Scottish Women case arisen in New Zealand.
However, the learned Judge’s views on section 11 are mistaken. A careful analysis of the section’s terms and legislative history makes clear that it has no such effect. Section 11 serves an important but limited purpose: ensuring that statutes can address new situations not specifically contemplated when Parliament passed them into law.
For example, section 11 allows fraud laws enacted in the pre-digital era to apply naturally to computer-based crimes without changing their fundamental meaning. Similarly, statutes governing vehicles passed before the advent of electric scooters remain applicable to these new technologies. In each case, the law is applied to novel situations consistent with Parliament’s original intent.
What section 11 does not authorise – despite Justice Glazebrook’s protestations – is the reinterpretation of statutory terms based on judges’ perceptions of evolving social values.
The Judge’s error was addressed squarely in a reply from Oxford’s Professor John Finnis to Justice Glazebrook’s article. Finnis points out that section 11 (and its predecessor in earlier legislation) has only a narrow technical meaning. The provision is simply to ensure that present-tense expressions in statutes apply to future circumstances – not to authorise courts to redefine statutory terms based on perceptions of changing social views.
The distinction is crucial. Courts can and should apply existing statutory concepts to new circumstances within their original scope and meaning. But they cannot legitimately update the meaning of statutory terms simply because they believe social attitudes have evolved.
The former ensures laws remain relevant as technology and circumstances change. The latter effectively transfers lawmaking power from Parliament to the judiciary – an outcome that undermines both the democratic legitimacy of the law and the rule of law itself.
Lessons for New Zealand
Our Supreme Court would do well to heed the UK Supreme Court’s disciplined approach. The For Women Scotland decision demonstrates that courts can navigate politically charged issues while respecting constitutional boundaries.
What makes the UK case particularly instructive is the Court’s restraint despite the highly contentious subject matter. The definition of “woman” has become one of the most divisive social issues of our time. Yet the UK Supreme Court carefully avoided substituting its views for Parliament’s policy choices, focusing instead on the objective meaning of the statutory text.
Instead of straining statutory language to achieve perceived socially desirable outcomes, courts should focus on faithfully interpreting Parliament’s words. When statutes use terms like “woman,” “marriage,” or “family,” courts should interpret them based on their meaning at the time of enactment, not based on judges’ perceptions of evolving social attitudes.
This does not mean law cannot evolve. But in a parliamentary democracy, significant social policy changes should come through the legislative process, not judicial reinterpretation.
Parliament can, of course, amend legislation when social attitudes shift. That is precisely what happened with the Marriage (Definition of Marriage) Amendment Act 2013, which changed the legal definition of marriage to include same-sex couples. This democratic process ensures change reflects the will of the people expressed through their elected representatives – not the preferences of unelected judges.
The constitutional imperative
The UK Supreme Court’s approach to the definition of “woman” reminds us of a fundamental constitutional principle: courts should interpret, not rewrite, legislation.
When Courts stray beyond their proper bounds, the consequences extend beyond constitutional theory. When they strain statutory language beyond Parliament’s intended meaning, they introduce profound uncertainty into the law. Voters cannot reliably determine their legal obligations by reading Parliament’s words. Instead, they must try to anticipate how judges might reinterpret those words based on judges’ perceptions of evolving social values.
This uncertainty undermines the rule of law’s fundamental requirement that laws be clear and predictable. It also threatens democratic accountability by transferring effective lawmaking power from elected representatives to unaccountable judges.
Some might argue that judicial intervention is justified in cases where Parliament has enacted legislation that appears to conflict with fundamental rights or values. But this argument fundamentally misunderstands our constitutional structure. In a parliamentary democracy, it is Parliament – not the courts – that has the democratic mandate to make these difficult policy choices.
The Court’s role is to interpret and apply the law as Parliament has enacted it, not to substitute its own judgment for that of elected representatives. As the UK Supreme Court has shown, respect for democracy demands judicial discipline, not activism.
To read the article on the Law News website, click here.