I have been reluctant to reply again, working as I do for the competition. However to give some insider information on the approvals. Each concurrent course run requires 1.7 instructors under the CAA's rules. So for example we generally run 2 courses at a time, requiring 3.4 instructors, and have more than this available. Any school that is not covering this is risking its approvals and in the process your money.
Each instructor not only has to be internally monitored for quality by an approved QA system, but is subject to CAA monitoring at the annual inspection (generally will be the first inspection while the instructor is in the job, as it was for me, and randomly as time is available for any later inspections).