Keir Starmer has urged public bodies currently not enforcing the Supreme Court’s gender ruling to bar trans people from single-sex spaces “as soon as possible”.

The court verdict, handed down in April, deemed that the legal definition of the protected characteristic of “sex” in the 2010 Equality Act referred to “biological sex” only, so excluding trans people.

In response, the Equality and Human Rights Commission (EHRC), the UK’s equality watchdog, issued interim guidance which called for transgender men and women to be banned from single-sex facilities which matched their gender and, in some cases, from using those which matched their “biological sex”.

When asked at the NATO summit in The Hague if hospitals, universities and government departments should implement the findings of the Supreme Court into internal policies, the prime minister said: “We’ve accepted the ruling, welcomed the ruling, and everything else flows from that, as far as I’m concerned.

“Therefore, all guidance needs to be consistent with the ruling and we need to get to that position as soon as possible.”

Maya Forstater, the chief executive of gender-critical campaign group Sex Matters, said Starmer’s comment was an “important intervention from the prime minister” given the “huge number of public bodies failing to implement the Supreme Court judgement and therefore operating outside the law”.

She went on to say: “Political leadership is essential if women, whose rights are being stolen, are not to be forced to turn to the courts, where public bodies will end up losing – at great expense to taxpayers.”

The Supreme Court’s verdict was expected to have wide-ranging implications for the trans community, and the Scottish and UK parliament buildings, the Football Association, Financial Conduct Authority and England and Wales Cricket Boardhave already moved to ban trans people from single-sex spaces and services.

The EHRC’s public consultation period into changes to its Code of Conduct, which aims to “support service providers, public bodies and associations to understand their duties under the Equality Act and put them into practice” closes today. A mass lobby took place at Westminster last week, where trans people hoped to voice concerns to their MPs.

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The situation has left many trans people feeling fear for their rights, and Green co-leader Carla Denyer warned that the EHRC’s interim guidance would “act as a bigot’s charter”, with the potential to unleash “vigilante harassment, intimidation and violence against trans people when they try to use facilities in public spaces”.

Starmer has been criticised for flip-flopping on trans rights before, having changed his mind to say that he no longer believed trans women are women, and trans men are men.

Following the Supreme Court judgement, he told the BBC: “I welcome the decision, which has given us much-needed clarity, and I think for those now drawing up guidance, it’s a much clearer position. I’m really pleased the court has clarified the position. We can move on from there and that’s very helpful. I welcome that.”

Starmer went on to say that “a woman is an adult female”, and when asked by ITV West Country if he believed trans women are women, he replied: “I think the Supreme Court has answered that question. A woman is an adult female. It’s important that we see the judgement for what it is: a welcome step forward. We need to move [on] and ensure all guidance is in the right place according to that judgement.”

In 2020, Labour committed to introducing self-ID for trans people but by 2023, the party had shifted to a version of Gender Recognition Act reform that kept a “medical diagnosis of gender dysphoria”.

The Supreme Court case was brought against the Scottish government by gender-critical For Women Scotland, supported by author JK Rowling, following a lower court’s finding that sex was not limited to biology.