Here's a thought....
Assuming you want a JAA CPL....Go get the JAA SE CPL, then get an FAA PPL issued on the basis of your JAA licence. Add an FAA ME rating on, for around $200 per hour and 10 hrs. You can now fly ME aircraft in the US AND the UK at private level. When you want the CPL ME in the UK, you'll be proficient in ME procedures by virtue of the FAA ticket, which remains valid for 2 years and is "re-validated" by a simple BFR.
Cheers
EA