There are not that many. We do one (BCFT), Cabair do, Multiflight sort of do one, although I believe they still subcontract the groundschool, and I think there is one in Coventry. Obviously any opinion I give could not be taken to be objective, but if you want any details feel free to send me a PM.
However don't rely on opinion here - anyone you talk to will have only seen one school, and may not be who they seem. Visit the places, talk to the current students. You need to fnd somewhere you like. Above all NEVER PAY UP FRONT FOR FLYING. You should be able to pay after you fly. I know people who have lost £20,000 paying up front. I lost some £2,400 - unfortunately that small section has to be paid upfront, and my timing was bad.
Good luck!