It has rarely happened in the past, probably because most med schools have waiting lists and applicants on those will probably be offered a place before the university will put the course into Clearing on UCAS. The only Med course that I saw in Clearing was at Buckingham, which is a private universty with insane fees for Medicine.
Maybe look into a course with 'easier' entry requirements and look into Grad Medicine? Such courses would be Biochemistry, Biomedical Science, Human Biology, Pharmacy even. I think all of these choices and anything similar will set you up well for Med School if you have your heart set on it.