Hiya!
I've had my Writtle interview (and offer!) in November, but I haven't sent in my references to Harper yet (eek- been trying to get canine WE for ages, got a year of equine and week of dairy, but all the kennels around here haven't had insurance/ places for volunteering), so I'll be curious to see what other people say. Also, did you manage to get your references on headed paper? Mine just have addresses at the top, but they're not fancy!
I massively over prepared for the Writtle interview- it's very relaxed. There was 3 lots of 2 interviewers in different rooms. I don't think mine had actually read through my personal statement which put me off a bit as I didn't want to repeat anything I'd already said there. They asked very general questions, e.g. why here, why vet phys, are you on track to get predicted grades, and then some questions about what I did with my horse! The mathsy bit they asked you to prepare they just seem to ask how you did it- so nothing too scary.
I'd also bought references with me which they didn't ask for in the interview, so I ran back and gave it to them anyway (because why not).
I know from last year's forums, I think people got asked more technical stuff in the Harper interviews, e.g. how does a muscle contract.
I've got my Moreton Morrell interview for Vet Phys tomorrow- hoping they don't ask any technical stuff as we haven't covered any muscle stuff in Biology yet, so my understanding isn't that great.
Good luck anyway and let me know how they go!