https://goodlawproject.org/case/were-challenging-the-ehrcs-interim-guidance/
The GLP page seems to have their skeleton argument up here, under a 'redacted amended' document embedded in the page.
Headings:
Ground 1: the Guidance misstates the law
Ground 2: in publishing the Guidance, the Commission has acted in breach of its statutory duties under sections 3, 8 and 9 of the Equality Act 2006
Ground 3: in the alternative to Ground 1, the statutory framework or part of it is incompatible with the Convention rights of trans people
(Each heading has extensive burble following.)
Remedy 112. The Claimants seek the following remedies: a. A quashing order, quashing the erroneous elements of the Guidance; b. A declaration that the Guidance is unlawful because it misstates the law and authorises and/or approves unlawful conduct; c. A declaration that in preparing and publishing the Guidance, the Commission acted in breach of its statutory duties under sections 3, 8 and/or 9 of the EqA 2006;
There are more remedies listed, including 'costs', but I can't copy paste them all, sorry.