Good driving schools in Maida Vale Watch
I would suggest that you go independent, and avoid the large driving schools - especially BSM. This is not some statement made on the quality of the instructors in each, as I had a fantastic instructor with BSM (as well as one who failed to turn up at all) - the instructors simply pay the franchise; they are self-employed. Rather, the larger schools are exploitative of both customers and instructors.
From your perspective, customer service will be a nightmare (your custom is actually a drop in the ocean to a national organisation, and the impersonality of it means that they just want your money; your results go by the wayside as far as the company's concerned). They also are more expensive to you, and here's why: you pay not only the self-employed instructor, but also the franchise, due to their extortionate fees to the instructors to allow them to use the BSM franchise, car etc. With an independent, you pay one person: your instructor - that simplicity means that not only is it (slightly) cheaper for you, but also that they get a much better deal of it. That excellent BSM instructor I mentioned? He had his pupil numbers decreased by the franchise until he could no longer afford to pay the company, so that they would allow him to make a living. It's an entirely backwards system, and some instructors with schools might therefore want to try and delay your test so that they don't lose a pupil and can still afford to pay the franchise.
Tl;dr: You'll get good and bad instructors with each, but the independents generally won't screw you or the instructors over so much as the franchises will.