Getty ImagesThe Equalities and Human Rights Commission (EHRC) has released interim guidance on how organisations should interpret the UK Supreme Court's ruling that a woman is defined by biological sex in law.
The new guidance says that, in places like hospitals, shops and restaurants, "trans women (biological men) should not be permitted to use the women's facilities". It also states that trans people should not be left without any facilities to use.
The EHRC said it was releasing interim guidance because "many people have questions about the judgement and what it means for them".
Guidance on when competitive sports can be single-sex will be published in due course, the EHRC said.
Last week the Supreme Court found the terms "woman" and "sex" in the 2010 Equality Act "refer to a biological woman and biological sex".
This means, for instance, that transgender women, who are biologically male but identify as women, can be excluded from women-only spaces.
As part of the judgement, Supreme Court judge Lord Hodge stressed that the law still gives protection against discrimination to transgender people.
The EHRC - which enforces equalities law and provides guidance to policymakers, public sector bodies and businesses - said the impact of the ruling was that "if somebody identifies as trans, they do not change sex for the purposes of the [Equality] Act, even if they have a Gender Recognition Certificate (GRC)".
In this respect, the EHRC says, "a trans woman is a biological man" and "a trans man is a biological woman".
The guidance also states that "in some circumstances the law also allows trans women (biological men) not to be permitted to use the men's facilities, and trans men (biological woman) not to be permitted to use the women's facilities".
When asked to clarify this, the EHRC pointed to a section of the Supreme Court ruling stating that trans men could be excluded from women's facilities "where reasonable objection is taken to their presence, for example because the gender reassignment process has given them a masculine appearance or attributes to which reasonable objection might be taken" in the context of a women-only service.
The EHRC guidance adds: "However where facilities are available to both men and women, trans people should not be put in a position where there are no facilities for them to use."
Where possible, mixed-sex toilets, washing or changing facilities should be provided in addition to sufficient single-sex facilities, according to the guidance.
Alternatively, the guidance says it is possible to have toilet, washing or changing facilities which can be used by all, provided they are "in lockable rooms (not cubicles)" and intended to be used by one person at a time. One such example might be a single toilet in a small business such as a café.
In schools, it says: "Pupils who identify as trans girls (biological boys) should not be permitted to use the girls' toilet or changing facilities, and pupils who identify as trans boys (biological girls) should not be permitted to use the boys' toilet or changing facilities. Suitable alternative provisions may be required."
In associations - groups or clubs with more than 25 members - the EHRC says "a women-only or lesbian-only association should not admit trans women (biological men), and a men-only or gay men-only association should not admit trans men (biological women)".
The EHRC says the interim guidance, published online on Friday evening, is intended to highlight the main consequences of the Supreme Court judgement.
"Employers and other duty-bearers must follow the law and should take appropriate specialist legal advice where necessary," it adds.
A two-week consultation to seek views from "affected stakeholders" is expected to be launched in May.
The EHRC aims to provide an updated code of practice to the government for ministerial approval by the end of June.
A government spokesperson said: "We welcome the ruling and the clarity it brings for women, and service providers.
"We will review and update policy wherever necessary to ensure it complies with the latest legal requirements."
