If the instructor isn't paid then there is no problem. The DfT told me this very clearly.
Cathar has been here before, warning of this and that, but there are so many axe grinders hanging about the N-reg training scene (with a wide variety of motives, none of which are ever disclosed) that none of these posts can really be relied on on their content alone, without careful checking.
What got this business going was the well publicised prosecution of D Kenyon. Prior to that, virtually nobody knew that the DfT would routinely hand out the training permissions to owners. It was during the court case that this amazing fact came out. Neither the CAA nor the DfT ever publicised it prior to that, which is quite bizzare since one would assume it is in their interest for people to remain within the law.
In the end, none of this really matters because those who can't arrange for an instructor to do it FOC will take a cheap flight to Florida
And exactly who benefits from that? Exactly nobody (outside Florida, of course).