The key point is that a court case has just happened which said that a GRC changes sex for all purposes.
This conflicts with what most in Parliament thought it meant at the time, and the position of the EHRC.
The simplest way to untangle this is for Parliament to be clear what it means by a simple amendment to the Act.
Haven't we've gone over Haldane's judgement before? As it stands the UK government and the EHRC position is that the equality act allows trans folk even with a gender recognition certificate to be barred from some single sex spaces/services. To use the EHRC summary:
There are circumstances where a lawfully-established separate or single-sex service provider can prevent, limit or modify trans people’s access to the service. This is allowed under the Act. However, limiting or modifying access to, or excluding a trans person from, the separate or single-sex service of the gender in which they present might be unlawful if you cannot show such action is a proportionate means of achieving a legitimate aim. This applies whether the person has a Gender Recognition Certificate or not.
That has still to be tested and a precedent set in court.