Hey, im studying Msc at Southampton. I would say that if your anatomy and physiology is not the greatest than a BSc would probably be better.....unless you are an exceptional learner as the level of knowledge expected is quite high....saying that, it is possible. Most people on the course decided to do the MSc as it is 2 years instead of 3 but it doesnt really work out much shorter when compared to academic terms.
As far as I remember there was alot of emphasis on doing an MSc over the BSc....so definitely make sure you know why you would rather do the MSc! I was also asked how I think I would cope with the demands of the course and how would I go about acheiving this. I was asked about my experience, why I wanted to do physiotherapy and why particularly at this uni. I was also asked about my last degree and specifically what I did for my dissertation and if I was to do it again what would I do differently.

Hope thats of some help!

If you are confident that physio is for you im sure this will portray in your interview.....
I was also asked where I thought I could see myself in 5 years time and what my aspirations were....

Good luck!