I don't think such collusion would be enforced though because the value of the total business is below the regulatory radar.
I see the point both ways and don't really have a view one way or the other, but one big problem with the UK PPL training business is that a cheaply run operation, using some poorly maintained junk, and employing (or run by) somebody who will turn up 7 days a week even when its OVC002 just in case somebody phones to book a pleasure flight for somebody's birthday, etc (which let's face it describes the majority of the present scene) will always undercut somebody trying to sell a slicker product based around a better organised school, better instructors, better/newer planes.
The only way around this is for the airfield to limit the # of fixed wing training ops to ONE, and make sure that ONE is doing it properly.
Instead, most airfields want to maximise their income (which, in the PPL context, comes mainly from banging endless circuits) and they allow an unlimited # of schools to set up. These regularly exhaust the market potential and go bust, leaving a stench afterwards.