they are regulated by the CAA :
Welcome to the UK Civil Aviation Authority.
There are several ratings which the instructor needs to have current before they can teach.
The aircraft ones and the instructor rating which is valid for three years. They have to do a days ground theory and either extend by experience or by test the test must be done every 6 years.
And no there is nothing like ofsted which monitors the quality of there training. The CAA doesn't either.
If you think your going to be able t complain about a school and something be done your going to be disappointed. The flight training industry has many talented people who proved a quality service. There are also your schools which to be honest are a bunch of rip off merchants.
If you have a complaint you would be better complaining to trading standards and even then I doubt anything will be done.
Best way is to hit them in the pocket and public air the dirty washing then people won't use them.