We've said this before, but it bears repetition. Way back in the early 2000s a UK national went all the way through the courts and ended up at the European Court of Human Rights seeking the legal right to marry their partner, and won. The person concerned was male, identified as a woman, and wanted to marry a man. This was impossible at the time because birth certificates were required and same sex marriage was not allowed in law.
One way round this would have been to introduce same-sex marriage, but the Labour government felt the UK public was not ready to accept that. (A mistake, I think. Civil partnerships were very readily accepted a few years later when the Tories introduced them.)
Instead, they drew up the Gender Recognition Act, making it possible for people with a psychiatric diagnosis of gender dysphoria to apply to a panel for permission to get a new birth certificate showing the sex they identified with, not their actual biological sex as recorded on their original birth certificate.
Like most British people, I was barely aware this was happening at the time. The House of Commons and the House of Lords had to debate the proposed new law but they weren't given a lot of time to do it, because the government had a big majority at the time and knew they could get this through with minimal opposition. Some MPs and Lords did raise concerns, all recorded in Hansard, but the government's response was (more or less) that this was scaremongering. They were doing this to be kind to a tiny minority of people. Their own experts said there were unlikely to be more than 5000 people in the whole of the UK who would qualify for a gender recognition certificate. They were spot on there, as in nearly 20 years it's been barely more than that issued altogether, I believe.
However, what the government had totally failed to grasp was that activists regarded the GRA as a foot in the door and never intended to stop there, and of course they didn't, as we have seen in the last few years. Self-ID was always the goal, and if you take away the safeguards of panel, psychiatric reports, gender dysphoria diagnosis and so on, and the effect of social media and social contagion, suddenly there are hundreds of thousands of people who don't identify as their birth sex.
Anyway, going back to the debates - having waved aside all concerns about single-sex services and spaces, women's sport, integrity of birth records etc etc - Parliament did make at least one amendment to the GRA before it passed into law. Getting a GRC would have no effect whatsoever on the individual's right to inherit a peerage.
Suppose Lord Marmaduke Bloggs has three children: daughter Araminta, son Josiah, son Ebenezer, born in that order. Josiah is the one in line to inherit the title, as the elder son. If Josiah predeceased Marmaduke, Ebenezer would inherit. Araminta has no chance, because she is a girl. Ludicrous system all round, but that's what we have.
Now suppose in adult life Josiah identifies as trans and takes the name Josie Bloggs. Josie gets a GRC and has a new birth certificate showing that Josie Bloggs is female. Marmaduke dies. It might have been expected that the title would now pass to Ebenezer. Josiah is legally female for all purposes now, after all - but no! Legally female for all purposes, except inheritance of a title! So the title that couldn't pass to Araminta still goes to Josie.
And naturally enough, if Araminta also got a GRC and became Aramis Bloggs, certified male - yes, you've guessed it. Still not entitled to inherit a title, in spite of being legally male and older than Josie.
What a farce.