Existing NHS guidance on the treatment of transwomen patients will have to change, the Equalities watchdog has said.
Baroness Kishwer Falkner, the chairwoman of the Equality and Human Rights Commission (EHRC), on Thursday said health bodies will be pursued if it they do not make changes and “conversations” on updating exiting rules will be had with the NHS.
It comes after the Supreme Court's ruling on Wednesday that the definition of a woman in equality law is based on biological sex, excluding people assigned male at birth who transitioned later in life.
Current NHS guidelines state that trans people should be accommodated in single-sex accommodation according to their gender identity, rather than their assigned sex at birth.
Baroness Falkner added that the court ruling means transwomen cannot use single-sex female toilets, changing rooms or compete in women’s sports.
"They (the NHS) have to change it”, she told BBC Radio 4's Today programme. “They now have clarity.
"There is no confusion as of yesterday, at 10.30 in the morning, and they can start to implement the new legal reasoning and produce their exceptions forthwith, but they have to change it. We will be having conversations with them to update that guidance."
Asked if the EHRC will pursue the case if it doesn't, she replied: "Yes, we will."
On changing rooms and toilets, Baroness Falkner added: “Single-sex services like changing rooms must be based on biological sex.
“If a male person is allowed to use a women-only service or facility, it isn’t any longer single-sex, then it becomes a mixed-sex space.
“But I have to say, there’s no law that forces organisations, service providers, to provide a single-sex space, and there is no law against them providing a third space, an additional space, such as unisex toilets for example, or changing rooms.”
Green MSP Maggie Chapman said the ruling had left transgender people "worried that people are coming after their right to exist".
The court handed down its decision in a long-running case brought by campaign group For Women Scotland against the Scottish Government.
The case started as a challenge to the inclusion of trans women in the Gender Representation on Public Boards (Scotland) Act 2018 and judges unanimously decided the definition of "woman" in the 2010 UK Equality Act relates to biological sex.
The case is expected to have wide-ranging repercussions for trans people accessing the services in their acquired gender.
In handing down the decision, Lord Hodge stressed the ruling should not be seen as a victory for either side, but politicians and other supporters of the groups have declared it as such.
Speaking to BBC Radio Scotland on Thursday, Ms Chapman said transgender people fear what could happen after the judgment.
"What the judge said yesterday morning about this ruling not being taken as a victory, the response by For Women Scotland and associated groups yesterday was very, very clear," she said.
"They are taking this as a victory and I think that's something quite potentially dangerous about where they go next.
"We've already heard people say they want to repeal the Gender Recognition Act 2004 and trans people are worried that people are coming after their right to exist."
