Actually, I think Hanora50 is partly right as the number of girls being referred to clinics like the Tavistock has sky rocketed, though I don't know how that affects the overall number of FTT.
It's worth thinking about why that might be, however, and one very obvious point is that going through puberty for girls is, I believe, now worse than ever before. Girls self esteem peaks at 9 years old. That is an awful state of affairs. Presumably,after this age, girls start to realise that their bodies are no longer their own, they are public property for all and sundry to comment on, gawp at, grope, and be told what your body should and shouldn't be like.
No wonder girls start to hate their developing bodies, no wonder they look for a way out of this hateful state of affairs. Back in my days girls who really struggled with puberty turned to eating, or not eating, as a away to control that development, to slow it down, take it away, take control. Nowadays there's a new name for hating your womanly body - gender dysphoria.
I am not in the least bit surprised that the numbers of girls identifying as anything other than female has gone through the roof. I think everyone's time would be considerably better spent in addressing what lies behind that jump in referrals. That does involve looking at the bigger picture, not focussing on the individual, though, which doesn't seem very popular.