I have just finished my 3rd year of a four year degree and I know I want to do a PhD. If I were to apply this autumn would I get a conditional offer like applying for a undergrad course or is it done on grades this far?

Funding is usually dependant you you getting a 2(i) or a 2(ii) plus a relevant Masters degree. This is a condition of the grant awarding body and will apply to all applicants irrespective of there ability to do the PhD. You therefore need to be aiming for a 2(i) if you want to start a PhD straight after your first degree. If you are studying a subject outside of science or engineering then you will probably need the masters degree as well anyway.