If you check the relevant links here, you'll find information about the various routes into both medicine and dentistry, including graduate entry:
http://www.learndirect-advice.co.uk/helpwithyo urcareer/jobprofiles/category28/
Chris
(PS: When I was at college we had a lecturer who had completed his first degree in mathematics and then gone on to acquire his MSc and PhD. During his first year as a college lecturer he decided that he wanted to go into medicine and made some enquiries about this just before Christmas. He was told that if you could study the A-level Biology course, in his own time, and achieve grade A, he would be accepted for the course. He took the Biology exam just a few months later and resigned from his lecturers job while crossing his fingers that he'd done well enough. Fortunately he did. Of course, this doesn't prove that the person you're referring to will be accepted but perhaps it does show that there might be a chance).