I had the double jaw surgery when I was 17, during October half term. I would say to anyone considering it, be careful when it is scheduled! I had a pretty easy recovery, and I found it hard with school.
about the liquid diet, I think those first few days were fine, as you're not really thinking much, plus the hospital does give you morphine! I lost nearly 2stone in 3 weeks... Def upside!
also I think there would ever be any problems with having it on the nhs. I know a woman who had it in her40's! Plus when I was 17, the surgeon told us, at that stage mine was 80% cosmetic, 20% medical, 5 years later it would've been 50/50, and so on! I had more trouble trying to get my insurer to let me go private!!!