UPDATE ON LAST POSTING: It still is the case that you can hire a 'G' registered aircraft with a FAA PPL so long as you remain within the UK.
I was hopeful that since becoming fully JAA that you may be able to travel outside of the UK, but you still cannot - Seperate issues.
With regard to the main topic - it has taken several years to integrate into the JAA system and not feasible to back-peddle now. However, AOPA have worked out a UK National Licence for PPLs to try and keep the costs down for enthusiasts