You would need to apply when you are in your third year if you want to start the vet course straight away with no break, or you could obviously have a break in between the two courses if you wanted.
Nottm and RVC are currently the only two who charge standard fees to grads (circa £3290), Cambridge I think charge that amount as well, and then college fees on top. Whereas all the others are £18000 py plus up to Edinburgh which is about £22000 py.
Some do a four year accerlated/2in1 course. (RVC, Liverpool, Edinburgh for definate, not sure about the others). Nottm are still a five year course.
It tends to be fairly easy to get offers from the expensive places - Edinburgh seem to give every grad applicant an offer (they don't even interview grads), quite a lot of grads get offers from Bristol, Liverpool etc. Nottingham seem to give very, very, few grad offers out. RVC give out a fair few - but have a huge number of grad applicants.
So, you need to make sure that your application is as competitive as it can be. I would suggest you don't rely on just your degree as you current 'work experience' - get other placements done as well during your uni holidays. Also, what alevel grades did you get first time round? Because if you got particulary low grades it might be worth resitting chemisty as well as your degree (there are people here you got C/D in chem and ended up taking chemistry a level again to get in).