You described it as a U-Turn in your initial post which it clearly is not. As you say yourself, in May they hadn’t decided whether it would be a GP or a specialist in gender issues. As mentioned in the article this is not much different at all to what they said last year.
Here is an article from last year outlining the plan to change to only having a single registrar make the decision. Notice that nothing is mentioned about it being a GP that knows the person. Their position has basically not changed yet you are calling it a u-turn.
Party chair says since act was passed by party in 2004, there is now a ‘much better understanding of the barriers trans people face’
amp.theguardian.com