Section F, part 3 of LASORS describes the MEP (Land) requirements. Read it
www.caa.co.uk/lasors
Standards Document 31 is a list of CAA-approved FTOs containing those who are eligible to provide JAA MEP ratings. Again read, you should be able to spot the US businesses.
http://www.caa.co.uk/docs/33/SRG_FCL_APPROVEDFTOS.PDF
This also lists those US schools providing CPL courses (JAA, approved for issue by CAA)
Given the prices, why not do it in the US if you are already there and have the relevant visa for training?