In answer to the question in bold, U.K. schools do not prepare you for USMLE. At least not specifically in the way that American and Caribbean schools do: it's not their job to prep for a foreign exam. They have their own style and content. It is an excellent medical education and in that way will help towards USMLE; but you will have to put in some extra time yourself studying for it.
Originally Posted by medgirl7
As for pass rates, you might get some figures for the Caribbean but there won't be any available for U.K. schools - too few people taking USMLE from each school and little interest in collecting the data.
"Ever tried. Ever failed. No matter. Try again. Fail again. Fail better."
Samuel Beckett, "Worstward Ho", 1983