Heh there
I would recommend a day travelling to the schools close to you and get a feel of them. You will be spending a great deal of time, money and effort to do your PPL and so it needs to be in a place you feel comfortable and confident. A couple of key questions to ask:
1.) Is there a tower here or is it air/ground only (a tower is generally better because you'll get used to talking to air traffic control faster but some people like air/ground because it is more laid back)
2.) Will you get to stay with the same instructor or 2 instructors throughout your training (this is better for continuity and saving you money in the long-term)
3.) Does the "package price" they offer include landing fees, VAT, instructor charge, test fees, ground school, books, - what are the extra costs that you can reasonably expect to pay
4.) After you get a PPL is there a way of getting involved in trips with other members. Are there any social aspects to the club?
5.) Will you be given the option of pre-payment or paying on the day? (this can be important if you don't know the financial viability of the club or if you would prefer to know its paid for!)
6.) Can you see the type of aircraft you will be training on - can you see around the building, hangars etc?
Near your area to try:
West London Aero Club (at White Waltham which is just off the A404 between the M40 and M4 near Maidenhead)
Pilot Flight Centre at Denham
Airways Aero at Wycombe Air Park (just off M40 jcn 4)
Wycombe Air Centre at Wycombe Air Park
My advice - Wycombe Air Centre but only because that's where I trained and I think the place has a good vibe, the instructors are very friendly, the reception staff are top-notch, full tower, well-kept planes, tarmac runway (important in the winter!), etc etc.
Good luck and have fun!