Sorry, FatFlyer, you are wrong. There is nothing in the ANO to ban passengers from handling the controls. I believe there may be (probably is, in fact) something like this in EU-OPS... but that doesn't apply to private flights.
I will quite gladly admit to being wrong if you can provide me with a reference.
As for your scenario of passenger screwing up a manoevre and damaging the aircraft, the captain is responsible for the safety of the aircraft. As captain, you have to decide if you can guarantee the safety of the aircraft. If you can't, then don't do it. Most PPLs are quite capable of figuring out when a passenger is messing up most manoevres (I'm not talking about aeros here) and taking back control while it's still well within their capabilities to do so, especially if that passenger is also a PPL and especially at a safe height. But at the end of the day, it's up to the P1 to decide what he's happy to do, based on what he's sure he is capable of doing safely.
FFF
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