Had I looked at the forums last week in more detail I could have asked this question as I was at the CAA on Thursday.
And what do you really think the answer would be?!?
Q: Dear regulator, can I as a vanilla PPL without any instructing qualification let any passenger take control of my aircraft?
A: Dear PPL of course you can just be careful out there, and if things do go wrong just quote that you did so on my say-so.
People are trying to find reassurances where non exist.
If anyone wants to let a passenger 'have a go' then you do so at your 'peril' and if things go 't*ts up' then it is on your head.
I think that it is safe to say though that the chance that you get 'caught' by the airway police are pretty slim.
FD