Religion held by a person is a protected characteristic. So it’d be wrong of you to say, sit at work and rant about Christianity and mock it on front of a deeply Christian colleague, or prevent her from worshipping/subject her to discrimination etc.
Butvit wouldn’t be wrong of you to criticise the religion itself in as harsh a way as you like in a general sense on MN. It wouldn’t be wrong to say, wrote a sitcom about three priests in a parochial house on a small island. Or write a cartoon where Mohammed and Jesus sit in the pub rather a lot and discuss life.
The protected thing isn't the religion itself, it’s the people who hold the religion. And that’s right and fair.
So it’s the same with this issue. Abuse of, discrimination at work against etc of someone who is a transwoman or transman is wrong. The law protects them because of their protected characteristic.
It does not protect the ideology itself
No ideology is immune from discussion in the uk. None is immune from criticism, mockery, humour, sitcoms or anything else. The ideology is an abstract. The people are what are protected.
What’s happening at the moment is akin to religious people trying to ban blasphemy. Blair tried it. Luckily the idea was shot down.
Now I don’t know about anyone else, but I’d prefer not to live in a theocracy, they tend not to be terribly nice places.