You can try to get your US training approved in the UK, but it's by no means a sure option, but very much on a case-by-case basis. Also, the UK has recently tightened immigration rules, so the employer now has to prove that it is unable to find a suitable UK/EU candidate for the job. As far as I understand, this procedure must be repeated for each job, which can become a real hassle if you're getting locum positions.
However, the safest option would be to check with the General Medical Council and the British Medical Association. They would have answers for your questions.