Prime Minister Sir Keir Starmer does not believe transgender women are women, his official spokesman has said.

It comes after the UK Supreme Court ruled last week that a woman is defined by biological sex under equalities law.

In March 2022, when he was leader of the opposition, Sir Keir told the Times that “a woman is a female adult, and in addition to that transwomen are women, and that is not just my view – that is actually the law”.

Asked if Sir Keir still believed that a transgender woman was a woman, the PM’s official spokesman said: “No, the Supreme Court judgment has made clear that when looking at the Equality Act, a woman is a biological woman.”

The spokesman added: “That is set out clearly by the court judgment.”

Conservative leader Kemi Badenoch accused the government of having U-turned in reaction to the judgement, accusing Labour ministers of needing the Supreme Court to tell them what to think on the issue.

Pressed over when the PM had changed his mind earlier, his spokesman insisted the Labour government had been consistent that single-sex spaces “are protected in law”.

The ruling also makes it clear that a person who was born male but identifies as a woman does not have the right to use spaces or services designated as for women-only.

This means transgender women with a gender recognition certificate (GRC) can be excluded from single-sex spaces if “proportionate”.

The spokesman stressed the PM had repeatedly said “a woman is an adult female” before the court judgment.

In 2023, Sir Keir told The Sunday Times that for “99.9%” of women “of course they haven’t got a penis”.

Later that year he told BBC Radio 5 Live “a woman is an adult female”.

And in April 2024 he said Rosie Duffield, who quit the party last year, was right to say “only women have a cervix”, telling ITV: “Biologically, she of course is right about that.”

Sir Keir had previously been critical of Duffield’s views on trans people when she was a Labour MP, saying in 2021 that she was “not right” to say only women have a cervix.

Asked whether Sir Keir would now use a trans woman’s preferred pronouns, the spokesman declined to comment on “hypotheticals” but insisted the PM had “been clear that trans women should be treated with the same dignity and respect as anyone else”.

Earlier on Monday Sir Keir welcomed the court’s decision, saying it had given “much-needed clarity” for those drawing up guidance.

In his first public comments since the ruling last week, the PM told ITV West Country: “We need to move and make sure that we now ensure that all guidance is in the right place according to that judgment.”

Asked if he does not believe a transwoman is a woman, he said: “A woman is an adult female, and the court has made that absolutely clear.”

During a Commons debate on the ruling on Monday, Education Secretary Bridget Phillipson welcomed the “added clarity” of the ruling and said the government would work to “protect single-sex spaces based on biological sex”.

But Badenoch attacked Labour ministers’ previous record, accusing them of being “so desperate to jump on a bandwagon that they abandoned common sense”.

“I know what a woman is and I always have,” she said. “The people of this country know what a woman is.

“We didn’t need the Supreme Court to tell us that – but this government did.”

Badenoch added: “The idea that they have supported this all along is for the birds… They have never said this before, this is a U-turn, but we welcome it.”

Earlier, Philipson was pressed over whether a trans woman should use a women’s toilet or a men’s toilet.

“That should be on the basis of biological sex – that would apply right across the board to all single-sex provision,” she told BBC Radio 4’s Today programme.

“But the EHRC [Equality and Human Rights Commission] will be setting out additional guidance and a statutory code of practice because we need to make sure that everyone has the ability to access services that are safe and appropriate and respect their privacy and dignity.”

Phillipson added that “many businesses have moved towards unisex provision or separate cubicles that can be used by anyone”.

Asked whether there was unity in the Labour Party about this issue, she replied: “I speak for the government on this matter and I can be crystal clear with you that we welcome the ruling.”

Many Labour MPs will be uneasy about the comments from Sir Keir and Phillipson.

For now this appears confined to private frustration.

Some MPs who have campaigned in support of trans rights pointed to commitments in Labour’s general election manifesto to introduce a “trans-inclusive ban on conversion practices” as well as to “modernise, simplify, and reform” gender recognition law.

Those are still Labour Party policies, as far as we are aware, but any sign of backsliding on that and this debate may again become a tense one within Labour’s ranks.