Don't worry too much about how to present yourself as they will almost do that for you as you're going to have to provide proof of I.d etc.
Just make sure you know your p.s inside out and can talk extensively on things you have mentioned. Go through the websites of the schools you have applied to and make sure you know what makes Liverpool different to say Bristol, Nottingham or Surrey. Is it case based learning, modular or spiral in its teaching methods. Why do you feel Liverpool would be a good fit for you?
Then go through basic questions that may come up. It's a bit boring but bovine tb and badger culling are common questions. Where do you stand on that?? There are no right or wrong answers but you should know the basics and be able to express an opinion. Same thing for dog breeding standards with its associated problems, and why not Brexit and the associated problems with animal health legislation. Look at other topics that are specific to your interests. If they give you time to ask a question yourself, make sure the answer isn't on their website.
For the rest, just be yourself. They are not there to eat you alive, just to find out what makes you tick and how you approach a problem that you might not have come across in the past. So don't be afraid to say that you are not sure about something, but say that on the basis of what you have already seen or studied you would hazard a guess at.......
Good luck! You'll do fine!