I've got Chemistry at B so that must be minimum, but I don't think that was a factor. Long as you've got a 2:1 in a related subject, experience in a related field (I've worked in a care home but even shadowing a GP for a day, volunteering in a hospice or a job as a hospital porter and such like) and can show them that you're committed and pass the interviews. You'll need a fucking belter of a personal statement, I was told by a few careers folk and a couple of doctors that mine was a topper.
And also you need to be quite handsome. Naturally.