In England [UK complexity discussion deleted...] there are a number of
examination boards, each setting its own syllabus and examinations. Schools choose which to put their students in for, so they retain some choice of syllabus: it's common for a school to use mostly Board A but to choose Board B for a particular subject because they prefer Board B's syllabus for that subject. Most 18yos in England take A-levels, but many of the most highly selective schools have switched partly or completely to using the newish Cambridge Pre-U which is designed to have more headroom - someone who got a top grade at A level might not do so at Pre-U. There is coordination and control done by
Ofqual to prevent "race to the bottom" and someone (not sure who actually) ensures there's a core of material universities can rely on in maths, for example.
You can see syllabuses and sample papers at the exam boards' sites, e.g.
CIE. Here is a sample
Pre-U Chemistry set of papers - note that it does in fact include a multiple choice paper, but it's not that soft an option :-)
