"So if you take s19 of the GRA for example which says that a GRC "does not affect the descent of any peerage or dignity or title of honour," that means that the person with a GRC is effectively still treated as their birth sex for the purposes of the succession rules, and it is therefore an exception to the general position that people with GRCs are treated as their new gender/sex. It is an exception regardless of how it is phrased. It doesn't have to literally say that the person with a GRC is still their original sex for succession purposes, that is it's effect."
It is very sad that someone whom I think is a lawyer gets it wrong. Firstly, peerages are covered in s16 not s19 as @AllyMcBeagle states. So let's quote s16:
The fact that a person’s gender has become the acquired gender under this Act—
(a)does not affect the descent of any peerage or dignity or title of honour, and
(b)does not affect the devolution of any property limited (expressly or not) by a will or other instrument to devolve (as nearly as the law permits) along with any peerage or dignity or title of honour unless an intention that it should do so is expressed in the will or other instrument.
Firstly noted that although Ally claims this is an exception to the change of sex/gender, that the section itself refutes that and explicitly says that the gender has become the acquired gender (which by s9 reaffirms that sex has become the acquired sex). So s16 - not s19 - is definitely not an exception as claimed.
Moreover, Ally says, "that the person with a GRC is effectively still treated as their birth sex for the purposes of the succession rules," but there is nothing in the text of the statute to reflect that view. Subsection a) says nothing about the person who has changed sex. What it says is that the change of sex doesn't change already established lines of inheritance. Why should it? They are already set. Why should one person changing sex affect whether or not a second person inherits a peerage? It clearly should not. And that is what s16 says. It is a section about lines of succession and not about the person who has changed sex.
This is not an example that the change of sex hasn't taken place.