Fiona McAnena, the director of campaigns at Sex Matters, said the policy was “doing everything in its power to circumvent the law on single-sex spaces”.

“The term ‘legal gender’ has no basis in law or medicine, and it’s extraordinary that NHS bosses at West London think that they can test the law by writing rules using bogus terminology,” she said.

“A patient or staff member could have a good case if they decided to challenge the trust in court. But it shouldn’t take legal action by individuals for public institutions to ignore demands from trans activists and fulfil their legal obligations.

“If this policy is permitted to stand, other NHS trusts across the UK may follow suit. The sooner NHS England brings out a revised policy that complies with equality law and protects sex-based rights, the better.”

The Telegraph previously revealed how all NHS trusts in England were in breach of the law because of outdated guidance that allows trans women to use women’s spaces for both patients and staff. There is no evidence that any trust is yet to operate their guidance in line with the law.

A spokesman for West London NHS Trust said: “Our policy is a temporary version while we await national NHS guidance. It reflects the Supreme Court ruling, and we have used legal advice to help make sure we balance the rights of each protected individual or group while maintaining our ability to provide safe and effective care.”

An NHS spokesman said: “The Equality and Human Rights Commission’s statutory guidance has been laid in Parliament, and we are reviewing it with the aim of publishing draft guidance for the health service shortly.”