You can Google the NHS "rules" re braces.
DS one was refered by our dentist several years ago, once all his baby teeth had fallen out (I think he was 13) The orthodontist said DS is so sever he needs surgery which can't be done untill he's stopped growing/18.
At the last visit DS had just turned 16, and I was asked a lot of questions regarding whether he has finished growing, but I don't think any 16yo boy has, and thought the orthodontist should know this. DS has a 5.2 grandfather, and a 6.2ft great grandfather and uncle, so how should I know how tall he will grow?
Anyway, he's never had a brace as it won't even touch what needs to be done, although they will fit one when he's 17 if he does want surgery. Which we've already decided he won't (cosmetically there is no need, and Ds tells me he's not in pain, despite a massive under-bit. Think Buzz Lightyear)
DD is 10, and I shall be asking the dentist next week about referring her. I think it's probably all cosmetic with DD. How, I don't know as DH, I and extended family all have perfectly straight front teeth.
Sorry, that was long and probably not very useful. In our area, I think there is only a few months between dentist referring and and seeing the orthodontist. I suspect we may have to pay £2-£3K for DD's teeth. 