Oxford and Cambridge don't use the UKCAT, their admissions test is the BMAT (UCL and Imperial also use BMAT). Unfortunately you don't get the results of the BMAT prior to applying. Applicants must apply for medicine by 15th October, register for the BMAT by September (from memory) and then they sit the BMAT (from memory) in early November and get the results a couple of weeks later.
Oxford places lots of emphasis on the BMAT, especially s.2. Some colleges score their applicants by alloting a percentage score of GCSEs at A* for half the mark and a score for their BMAT result for the remainder score. This is how they decide whom to invite to interview.
Lots of med schools operate UKCAT cut offs. At Sheffield for example, the cut off score for the previous two years for UKCAT has been 720, they don't invite people for interview under that score, no matter how good the rest of their application.
What are his A level subjects? The vast majority of Oxford medics study A levels Chemistry, Biology, Maths and something else on the Trinity list (preferably Physics). Were his AS results at A grade, well into th 90% plus scores?
Some med schools use neither the BMAT nor UKCAT. Birmingham med school for example relies heavily on applicants' GCSE profiles. I think the minimum for Birmingham last year was 8 A grades at GCSE, though most successful applicants had many more than 8 A.
If I were him I would research very carefully, as success in getting into medicine is as much about applying to the med schools that match your application strengths as it is about being excellent across the board.