I am happy for you to log P1 and I will log nothing.
Which is perfectly correct if you are a passenger on any flight. God help us, do I have to check if you are down the back of a commercial flight and if you are going to log something simply because you have an instructor rating and are on board?
However, if an instructor is performing any function on the flight then they have to be a member of the crew and record their time as such......only option being P1 on a single pilot aircraft.
I would suggest that BOSE's statement of
Well if you are current under CAA/JAA regs and come and fly with me
Clearly indicates that it is BOSE who is inviting you along on their flight not the other way round. Do you get many passengers inviting you as the only pilot along on their flight? In private aviation is it not the pilot who brings other people along on the flight?
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I have asked about this system of pilots being "checked out" agreeing to be pilot in command. What I was told is that it is amazing in such a rush to sue culture that people would leave themselves open to ruin with absolutely no defence should an accident happen.
The reasoning was that you present yourself for a check flight because for whatever reason you are not happy yourself or the owner is not happy or the club rules require or for whatever other reason you like you can not simply take the aircraft and a passenger to go flying.
If you agree to be P1 and for example BoseX agrees to be simply a passenger, in the event of a fatal accident you can rest assured that BOSE's estate will sue your ass off because you took command of the aircraft carrying a passenger when you knew you should not have and by doing so were negligent.
From a legal point of view, in such a case your would be far better flying solo to regain currency. In other words do it with an instructor or someone else who is P1 or do it solo.
Regards,
DFC