I can't answer for UK schools, but in Australia the schools couldn't care less what your major is in. The only exception to that is Melbourne's revamped med school that reopens in 2010 (or maybe 2011). That school will require certain subjects to have been taken for entry.
There is no "liking" one over the other. However, all of my classmates who were non-science majors struggled terrifically the first two years, so any preference may simply be on the part of the faculty recognizing this issue.