Sam,
Bad management generally sorts itself out over time. Whether that's by a change of management as the owner realises the mistakes, or because they finally go bankrupt because the customers finally decide they've had enough! I don't think the CAA is particularly interested in such cases.
Some issues such as maintenance, number of hours the aeroplane has flown, weather etc... is quite common, some schools manage it better than others. But especially in the U.K. This is particularly hard to judge (due to weather). Instructors however seem a little weird... but that could well be just your particular school / club.
There are so many schools and clubs, especially around London. They are not all the same price, and you will need to look into each individually. I recommend a trial flight with each before signing up, and making sure that instructors and management seem nice, and of sound mind. They often will state a "plan of action" which most likely will waste at least 2 hours, but at least you will be in a new environment!
Where are you exactly? That may help us recommend places.