To get in as a vet nurse you need to either:
-Do a vet nursing degree, achieve at least a 2(i) and apply as a second degree. This usually incurs full cost fees (£16000 per year) however a couple of uni's are cheaper (£3000). But of course, the cheaper uni's are harder to get into as there are many more applicants.
-Do a VN qualification (takes two years), this gives you exemption from one A'level. You still need to take 2 A'levels (Chemistry and Biology) and achieve A grades at one sitting. If a university particularly likes' you, you may get a slightly lower offer, however they seem to be keen to ensure that the calibre of students remains similar between traditional applicants, and non.
I hope this is helpful. Remember policy changes from year to year, and there are now vet nurses in our vet schools, even though it wasn't that long ago that they weren't considered...