Finally a post on which I comment with a degree of authority!
You must have at least two years of work experience in the US before you can take the qualifying exam to transfer to English law (UK law does not exist - Scottish law is different). If you search BPP professional school on the net you can get info on the modules you have to take before you can qualify here.
Technically it's certainly possible, but if you're not working for a big international law firm, expect this tranfer exam to be taken with a certain amount of skepticism by many employers. This is because it is relatively new, and most partners in national firms will not be familiar with it, and will be concerned about a lack of experience in England.
The 'bar' exam does not exist over here. Training is different for solicitors and barristers.
Good luck to all!