The real answer is to use your FAA ASEL in an N-registered aircraft (there are plenty based in the UK) and then you can exercise the full privileges of your license.
You can also get an IR more easily and fly airways anywhere you please provided the aircraft and yourself are FAA registered. There are plenty of companies that will handle your N-registration in the UK.
The only point to consider is that if you are not the owner of the N-reg aircraft (i:e you are renting it from a third party) then this is illegal in UK airspace as it constitues "air work" unless the DfT has deemed it OK.
You can also get FAA medicals, BFRs and IPCs in the UK without too much trouble.
Converting to a CAA or JAA license is expensive and pointless (I know I did it 10 years ago) provided you can find an N-reg aircraft to fly.
