Kirstey "But I think I'm correct than one is absolved of rule 5 in order to keep the aeroplne safe?
or did I make that up!"
You are quite correct but if you do breach rule 5 in such circumstances you must inform the CAA in writing as soon as is reasonably practicable after the breach.
The reason for this is obviously to ensure that its not used as an excuse after the CAA have started investigating a low flying complaint.