BEagle,
Would you be so kind as to give us a reference to which specific JAR ratings must be held to fly aeros or formation?
To my knowledge there is none. Thus the 'check' pilot is performing no legally required function, only that required by the Club.
Funny you mention the PFA coaches. That system was inspired by the Tiger Club. Do check your history, old boy.
As MLS wrote,"I'm inclined to think that the only real criteria are experience and competence."
Don't think for a moment that the Club is operating outside of the law!