Ally, I'm a little confused here but it seems I was unnecessarily arsey
No worries at all! I think sometimes when I explain the law it can come across as if I endorse it. I have said in other threads that the law would be different if I was in charge. You just deserve to know what you are letting yourself in for if you stick with the pronouns that match the person's sex rather than go along with the one's that match their gender (incidentally, I don't have a big problem with the term 'misgendering' because my position is that gender is a nonsense concept, but I always avoid the term 'cis' because that one does bother me).
Specific in the sense they allow positive discrimination as a proportionate remedy?
There's not a generic provision saying positive discrimination is OK. There are some very specific provisions saying basically 'If you do X, it won't be discriminatory against people with Y characteristic' - eg you can do all women's shortlist's without men being able to complain they are being discriminated against. The language about all women's shortlists in the Act is a bit hard to read if you don't have an in-depth knowledge of the structure of the Act, but here's the provision about single sex services:
28(1) A person does not contravene section 29, so far as relating to gender reassignment discrimination, only because of anything done in relation to a matter within sub-paragraph (2) if the conduct in question is a proportionate means of achieving a legitimate aim.
(2) The matters are—
(a) the provision of separate services for persons of each sex;
(b) the provision of separate services differently for persons of each sex;
(c) the provision of a service only to persons of one sex.
So you can see that it's saying that whilst it would normally be discriminatory to treat transwomen with a GRC differently from women, if you're providing a single sex service and you've got a fair reason for excluding them (or in the fancy language of the Act it's 'a proportionate means of achieving a legitimate aim') then in that specific instance it doesn't count as discrimination.
In the same way, there are some specific exceptions which give special treatment to religious people, but they were no use to the registrar who didn't want to marry gay couples and ended up losing their job.