SNP ministers will argue for the rights of ‘pregnant’ men and male-born ‘lesbians’ at the UK’s highest court tomorrow in a landmark case about the definition of a woman.

The Supreme Court hearing will decide if biology or bureaucracy is key, with far-reaching implications for women-only spaces and services.

Feminist group For Women Scotland (FWS) is challenging Scottish Government statutory guidance on the definition of a woman linked to a 2018 Holyrood law. 

The Gender Representation on Public Boards Act was intended to create a 50:50 balance between women and men on quango boards.

It defined a woman as ‘anyone living as a woman’, including biological males with or without a gender recognition certificate (GRC), stating that they were female. FWS successfully challenged this in Scotland’s courts, arguing it impinged on Westminster equalities law.

SNP ministers dropped the definition from their law, but issued revised guidance that continued to say ‘woman’ included a trans woman with a GRC.

FWS is appealing the point to the Supreme Court in London.

Five justices, including the court’s Scottish president, Lord Reed, will decide if a person with a GRC saying they are female is a woman, for the purposes of the UK Equalities Act 2010.

Scottish ministers will argue such a person is a woman. In a 40-page statement, ministers insist references to a woman who is pregnant in the Equality Act would also apply to a ‘pregnant man’ who was born female.

They also submit it would be unlawful for an association of ‘lesbian women to exclude a person with a full GRC in the acquired gender of “female” who was attracted to women’. 

The Equalities Act says woman ‘means a female of any age’ and FWS argues this means it is based on biological sex, not ‘a bit of admin’.

Harry Potter author JK Rowling gave £70,000 to a crowdfunder for the FWS action, which has raised £200,000 so far. She said last week: ‘If a man is a woman, there’s no such thing as a woman.’

Susan Smith, of FWS, said the court ruling would have huge implications.

She told the Mail: ‘If we win, then we get a very clear-cut idea of who is protected and when. If we lose, it would make it almost impossible to keep a lot of spaces and services female-only, or indeed male-only, and Westminster will have a real mess to untangle.

‘You can’t get a certificate to say you’re a different age or have a disability you don’t, so ministers will have to think about why sex is protected in the first place.’

A Scottish Government spokesman said: ‘We cannot comment on a live legal case.’

Meanwhile, it has emerged that National Records of Scotland death certificates can record ‘men’ as dying of cervical cancer and ‘women’ of testicular cancer in line with gender identity, not birth sex.

The recorded genders are then included in official statistics data used by health experts.