I've been looking into this recently too, here the ones I have found.
UK FAA flight training
Eagle Flight Training - Flight Training at London Luton Airport
FAA Pilot Flight Training in the UK - Retford (Gamston) Airport
FAA Training - Courses Bonus Aviation Limited
FAA - Solo Flying School Humberside Airport JAA FAA
Willow Air Flying Club - Southend Airport, Essex UK
I've decided to go with Eagleflight as the rates are very competitive. The issue with doing the training in the uk seems to be the flight test. There is a uk based examiner but his prices are very steep (same as JAA). Other option is to wait for US examiner to come over which happens from time to time.
I would be very interested to hear if you find any others.