Mazzy, great idea to put your experiences on here. I'd thought about the same myself, so I hope you don't mind if I butt in on yours.
As a 10 hour student, now flogging around the circuit, I can't emphasise enough the importance of shopping around flying schools and doing some trial flights.
Check out the briefing (and briefing facilities), instructor - technical knowledge and instructing capabilities, and the aircraft. Not all flying schools have knackered planes and, whilst individual rapport is one thing, some instructors are definitely technically better than others. I tried several schools close to home, before ending up with a well known one (albeit a good 1/2 to 3/4 hour drive from home) at Wycombe. There I found good, very experienced instructors, very well maintained aircraft (even a nice livery for posing!) and excellent club facilities, where total flying costs are less than my local clubs'.
As a lawyer, I would never advise anyone to pay up-front - even for a heafty discount. Flying in the UK is often abortive - you may be forced (rightly) to go some time between lessons. Money spent now alway has a higher cost than money spent later - think about the real value and risk involved in that discount. Almost everyone at my club pays as they fly - after the lesson - for actual chocks-chocks time. Moreover, time spent student solo is charged at the solo rate.
And what about Thom v. Pratt. Well, I've only sat the air law so far (would have been embarassing to fail!) but I actually used both books. Thom goes into the detail, but Pratt is far more readable. Use both (if you can find them/afford it). I'm convinced the differences in emphasis, presentation and thus, improved understanding, can only make you a better and safer aviator.