I did my PPL, Night rating & IMC with Cabair Redhill/Biggin.
It's a very professional outfit, though not the cheapest.
What REALLY matters is to get an Instructor that suits YOU. the first one I had was simply dreadful, and I nearly gave up after 10 hours. The second was awesome, and if he was still doing it, I'd recommend him.
I guess that the above sentiment is true of any flying school, but it is particularly pertinent in an establishment like Cabair, where most Instructors tend to be wannabe airline pilots, and are using Cabair to get the hours they need. (In return, Cabair use them by not paying them particularly handsomely!) Try to pick an Instructor who is really interested in instructing, even though his/her mind is set upon something else.