I live near Blackbushe where the European Flyers debacle referred to above took place. I wasn't on the receiving end, but I know several people who were and I wouldn't have wanted to be one of them!
There are very few flying schools, no matter how big or well established, with which you should invest vast sums up front. If you absolutely insist, get hold of a copy of their accounts for the last 3 years or so and (if you don't understand them) ask someone who knows to explain the school's financial history and current financial risk. If the accounts aren't published and the school won't let you have them, don't place your money with it. Doing this at least allows you to make an informed judgment.
Paying up-front for a discount might seem attractive, but it is better to manage the funding for your flying yourself (and to view that experience as part of your career development).
The simple message is: If you give your money to a flying school in advance, you may not get your flying and you may never see it again!