The Conservatives have vowed to change the Equality Act to ensure “biological sex” is a protected characteristic.
The party said reforming the law – which states that an individual must not be discriminated against on the basis of their sex – would clear up “confusion” among public bodies and institutions about access to female-only spaces.
The Tories said it would change the Act to clarify that “sex” meant “biological sex”.
It said the shake-up would make it “simpler for service providers for women and girls, such as those running sessions for domestic abuse victims, to prevent biological males from taking part”.
The party’s latest general election promise came as it claimed that the current terms of the Equality Act, which came into force in 2010 after being passed by Labour, was outdated and had created uncertainty.
It could result in transgender women being barred from female-only spaces.
Prime Minister Rishi Sunak said: “The safety of women and girls is too important to allow the current confusion around definitions of sex and gender to persist.
“The Conservatives believe that making this change in law will enhance protections in a way that respects the privacy and dignity of everyone in society.
“We are taking an evidence-led approach to this issue so we can continue to build a secure future for everyone across the whole country.”
Equalities minister Kemi Badenoch suggested the government was considering the move earlier this year.
At the time, LGBTQ+ charity Stonewall said the proposal risked “opening yet another chapter in a manufactured culture war that will see little benefit to women, cis and trans alike”.
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Announcing the pledge on Sunday night, Ms Badenoch said: “Whether it is rapists being housed in women’s prisons, or instances of men playing in women’s sports where they have an unfair advantage, it is clear that public authorities and regulatory bodies are confused about what the law says on sex and gender and when to act – often for fear of being accused of transphobia, or not being inclusive.”
The Conservatives also said the proposed change would not remove the existing and continuing protections against discrimination on the basis of gender reassignment provided by the Equality Act.
The sex of those with a Gender Recognition Certificate will still align with their acquired gender in law outside the Equality Act, for example, marriage law, as is the status quo.
Under the new scheme, the Conservatives will also establish in law that gender recognition is a reserved matter, as they say “this will mean that an individual can only have one sex in the eyes of the law in the United Kingdom”.
The pledge comes as Labour prepares to put defence and national security at the heart of its election pitch to voters on Monday.
Sir Keir Starmer will describe Labour as the “party of national security” as he meets veterans and candidates during a visit to the North West.
He is also expected to reaffirm the party’s commitment to the so-called “nuclear deterrent triple lock”, which includes a commitment to construct the four new nuclear submarines in Barrow-in-Furness.
Meanwhile, the Liberal Democrats are set to call for new protections for rivers and coastlines to end what it describes as “environmental vandalism”.
The party has announced an expansion of marine protected areas and a new Blue Flag status for rivers will be included in its manifesto.