Nottingham student here - we can only resit a year if you obtain Extenuating Circumstances and get approved.
So you can fail, then everyone is entitled to a resit opportunity in the summer. If you fail this, I believe you have to leave the course. If you fail this but you have EC, then you can resit the year ONCE.
As far as I know this is quite strict compared to other vet schools, however I only know of two people having had this happen to them. Most people manage to pass the exams in the two chances they get, unless they have something else going on in life (hence the EC).
You get IMMENSE support from tutors, module convenors etc if you do end up having to resit an exam.
Hope this helps!