Seems to me that a lot of people have forgotten about (or not heard of) the saga of Michael Bentine's son (the actor) ....and the consequent highlighting by the CAA, at the time, of the wisdom of booking out, even for short sight seeing flights as mentioned by the first poster.
For anyone who doesent know the story Michaels son (whos name I cannot remember) went for a short jolly with a tug pilot at Lasham, in one of their tugs, and failed to return. The aircraft was not missed for several days and due to lack of information (not booked out) a subsequent search failed to find any wreckage. Eventually, the Super Cub was found some months later in a forest near Petersfield. Both occupants were still in the wreckage.
So, although not a perfect system, isnt it a good idea, legal or otherwise??
UV