Whether they had srs cannot influence legal judgements made under the equality act, as specified, the amount of 'meaningful' transition or none at all, is treated the same under the terms of the EA.
Also I have checked with official channels, there was no EHRC guidance updated last year that changed any limitations, exemptions or guidance regarding trans access to 'female spaces'.
There was quite a few fake EA 2010 accounts of a gender critical persuasion popping up on twitter trying to persuade people and business's of subscribing to illegal advice, or 'fake news' if you like, it seemed to take in some people searching for confirmation bias.
Trans people, possibly 100,000s are using the spaces that match their gender yesterday and stretching back, and will do tomorrow and beyond.
And if it was illegal, this simply wouldnt be the case.
So it is clearly not illegal, whether or not it inhabits some grey area of application is also mostly irrelevant, as nothing can be ruled on a blanket basis, and only a case-by-case.
Who decides case-by-case if someone wrongly enters a space?
Effectively, nobody. Occasionally you hear of somebody being thrown out, rarely, but importantly, you are far more likely to witness this event, than hear of an individual suffering personal harm because the Gender Re-assignment portion of the EA being abused.
Which as evidenced in the court case I linked, found it was illegal to discriminate a trans woman entering a female toilet. The Equality act explicitly does not require a GRC or Surgery.
You dont need to be able to tell the difference between good and bad legal advice in a situation such as this, occams razor will suffice.
Trans people are using these spaces now, under current conditions, and cause no harm.