The ruling by the five Supreme Court judges means that a woman is defined as someone born biologically female under equalities law. This will have implications for employers, and the government will need to carefully consider the decision in light of rules against discrimination at work and in places of employment, and review statutory guidance.

The case was brought by For Women Scotland, the gender critical campaign group, against the Scottish government, and centred around the question of whether a person with a full gender recognition certificate (GRC) which recognises that their gender is female, a ‘woman’ for the purposes of the Equality Act 2010.

The Supreme Court unanimously allowed the appeal. It held that the terms ‘man’, ‘woman’ and ‘sex’ in the Equality Act 2010 refer to biological sex. Lord Hodge, Lady Rose and Lady Simler gave a joint judgment, with which the other Justices agreed.

On interpretation of the Equality Act 2010, the ruling stated: ‘Interpreting “sex” as certificated sex would cut across the definitions of “man” and “woman” and thus the protected characteristic of sex in an incoherent way.’

The judges also determined that ‘a certificated sex interpretation would also weaken the protections given to those with the protected characteristic of sexual orientation, for example, by interfering with their ability to have lesbian-only spaces and associations’.

This also affects operators of separate spaces and single sex services, including changing rooms, hostels and medical services.

On protection from discrimination for trans people, the Supreme Court judges stressed: ‘This interpretation of the EA 2010 does not remove protection from trans people, with or without a GRC. Trans people are protected from discrimination on the ground of gender reassignment. They are also able to invoke the provisions on direct discrimination and harassment, and indirect discrimination on the basis of sex.’

Rob McKellar, legal services director at Peninsula, said: ‘Any clarity on how the law works is always welcome. The main takeaway here for employers is that although this ruling has confirmed that in the Equality Act 2010 the words “woman” and “sex” refer to biological sex, transgender people are still protected under the Act.

‘The ruling does not change the fact that employers should strive to provide an inclusive workplace that embraces and welcomes all individuals, regardless of any protected characteristics, and failure to do so could result in a discrimination claim at tribunal.’

The Equality and Human Rights Commission (EHRC) said it was reviewing the contents of its single sex services guidance to reflect the Supreme Court’s ruling.

Baroness Kishwer Falkner, chairwoman of the EHRC, said: ‘This judgment has significant implications for the interpretation of Britain’s equality laws. We welcome the clarity this ruling brings; its importance to those whose rights are affected under the Equality Act cannot be overstated.

‘We will take the outcome of this appeal into account in our ongoing work as the regulator of the Equality Act. That includes the development of our revised Code of Practice which, subject to ministerial approval, is expected to be laid before parliament before the summer recess.’

Trans rights campaigners said they were examining the judgment before deciding on their next steps.

Peter Cheese, chief executive of the CIPD, the professional body for HR and people development, commented: ‘This will provide further understanding for individuals and organisations in what has been a difficult area for employers to interpret and find the right balance, recognising the rights and beliefs that need to be upheld for all.

‘Employers will need to ensure that their policies and approaches are up to date with this legal clarification of the position in the UK. However, there will remain legal and practical issues for employers to work through to support inclusion, dignity, and fairness at work and ensure all colleagues are protected from discrimination and harassment.’

The government welcomed the ‘clarity and confidence’ for women and service providers, and will review the ruling to ‘make sure we are fully compliant with it’.

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