I think that if you know you want to practice law then you should just crack on with a Law degree rather than fannying around doing something that you'll 'enjoy' for 3 or 4 years, to be quite honest.
Oxbridge might statistically appear easier to get into [something like a 4:1 average] than some other courses at other universities but in reality it's more competitive because the quality of a lot of the applicants will be very high.