Pitts 2112, just a small point. You say that 'just logging hours is considered compensation' and indeed the CAA in the past have tried to argue this. Sometimes they were successful before some Benches; but not always.
However that cannot be the law as it stands today. There is no Divisional Court (Administrative Court if you prefer) or Court of Appeal authority upon the point but when the giving of flying instruction for reward was a privilege of the PPL it was (just) possible to argue that 'reward' covered flying hours other than instructional hours.
The position today is different. The PPL FI is in no special position in relation to flying for reward than his non FI PPL. If the mere logging of hours itself constituted a breach of the terms of the PPL then the FI could give no instruction at all and the rating would be meaningless.