This change is more or less exactly what I was expecting after reading the Cass Report, it's how shifts in civil service directions often occur. The fact that this isn't related to any specific messaging from the government in power is an indication that this is a technocrat/bean counter drive change, and those take years to work up as the institutional inertia keeps things chugging along in one direction. The Cass report would have been quietly quashed and downplayed if they were going to stay the course, but some internal discussions must have occured that decided to shift strategy, and they used it as marking the new framework moving forward (there's always a date or event that everybody uses to align). Now all the little government organs are realigning themselves. I'm sure the fact that places like Tavistock didn't agree to participate also irked quite a few bureaucrats, which is playing into the speed of the changes.
I also think there's been quite a bit of mutation in the trans movement over the last decade, in keeping with it being a social contagion. We joke about it often but how many times have you seen a troon saying they were an incel womanhater in the 00's. Because transitioning isn't real and there was no gatekeeping, and being trans became trendy, trooning went the way of all fandom, which is that it got flooded and optimized towards the most obsessive degenerate freaks, even worse than the average troon was a decade previously. Remember that formal transitioning has been legal in the US since the 70's, ditto the UK (though I think birth certificates were excluded in both cases). The obsessives and faggots of yesteryear where much more interested in keeping their heads down and being left alone. Not so this new crop.
I also think we can't discount Trump's effect on all this, or rather the effect that Trump derangement syndrome had on liberals in the US, and by extension places strongly influenced by US culture. This is anecdotal but I just don't remember the type of extreme zealotry in these debates prior to the military ban. It was at that point that a huge number of people decided to believe all trans people, all the time, because otherwise you were a cheeto-nazi. It was in the immediate aftermath of that that so many people talked about troons being denied "essential healthcare" because they couldn't get the military to foot the bill for their castration.