Medicine is offered at a large number of Universities. Recently there have been several new medical schools opened up meaning more positions are available. Most people study as undergraduates after studying A Levels (or equivalent), normally including chemistry and biology. However a growing number of places are available for postgraduates to come in a do a medicine course as well as pre-med courses for people who have not studied the traditional science A Levels normally expected for a medicine degree. All medical schools in the UK are overseen by the GMC.
Any entrance requirements listed are currently being updated for the 2008/9 application cycle and it's advised that you confirm this information for yourself before making an application.