I think this seems to be what they are attempting.
It is one of the edits which was added by Bridget Phillipson to the updated EHRC Guidance between September 2025 and May 2026. It is not in the current version - from 2022(?) And may never make it through the 40 days of prayers in the Commons, for the 2026 edition. But whether in or out of the guidance, the courts would look at the law.
From the EA2010:
14 Combined discrimination: dual characteristics
(1) A person (A) discriminates against another (B) if, because of a combination of two relevant protected characteristics, A treats B less favourably than A treats or would treat a person who does not share either of those characteristics.
(2) The relevant protected characteristics are— (a) age; (b) disability; (c) gender reassignment; (d) race (e) religion or belief; (f) sex; (g) sexual orientation.
(3) For the purposes of establishing a contravention of this Act by virtue of subsection (1), B need not show that A’s treatment of B is direct discrimination because of each of the characteristics in the combination (taken separately).
(4) But B cannot establish a contravention of this Act by virtue of subsection (1) if, in reliance on another provision of this Act or any other enactment, A shows that A’s treatment of B is not direct discrimination because of either or both of the characteristics in the combination.
(5) Subsection (1) does not apply to a combination of characteristics that includes disability in circumstances where, if a claim of direct discrimination because of disability were to be brought, it would come within section 116 (special educational needs).
(6) A Minister of the Crown may by order amend this section so as to— (a) make further provision about circumstances in which B can, or in which B cannot, establish a contravention of this Act by virtue of subsection (1); (b) specify other circumstances in which subsection (1) does not apply.
(7) The references to direct discrimination are to a contravention of this Act by virtue of section 13.
This looks to me that the combination of two protected characteristics have to be within one person. Not that each person has a separate characteristic that they don't share.
But it will depend on the labelling of the space. If the space is advertised as "Women plus TW" then they have not used the single-sex exception in the EA2010 and so there is no false advertising.
However, the question will be if there is indirect discrimination because of the removal of the historic single sex women's pond? That will depend on lots of things including the robustness of any previous consultation and what the founding principles of the ponds says and any rules about how to change that.
In practice we are going back to the early 20th century where men will colonise all the spaces and women will be pushed out. Which is why the EA2010 has these exceptions to protect against - it is just that has all been forgotten by too many people.
I still can't get over the idea that everyone knew what a woman was when we didn't count as "persons" under the law - and so we couldn't have anything for ourselves. Then after about 100 years of hard won rights along came the EA2010. And it seemed for a short while that the structural barriers were gone and we would only have to overcome unconcious bias.... But then somehow sex suddenly got complicated and noone knew what a woman was any more - so we couldn't have anything for ourselves - all over again. Funny how it always seems to work in favour of the male sex?