You can not pay anyone to comitt an offence.
You can not charge a UK citizen one amount and a French citizen a different amount for the same product.
You can not charge a White Man one amount and a Black Man another for the same product.
If the big A flying club charges 100 per hour aircraft hire and 50 on top for dual instruction.
Mr B Student has a CPL holding instructor and pays £150 ( 100 for the hire of the aircraft and 50 for the service provided by the instrutor - flight instruction)
Mr A Student has a PPL instructor and if what you say is true they pay £150 for the aircraft hire.
Is it not true that Mr A is being overcharged because Mr B only pays £100 for the same thing?
On what basis do you discriminate against Mr A Student by charging them more when you have advertised the aircraft hire rate as £100?
Never mind the legality it is what most people call a rip off and even bigger one if you get your PPL application refused because the person who trained you did it illegally.
Regards,
DFC