Metman,
You are quite right, The overwing exits are classed as "self help" exits, and the CAA requirement is that at least one ABP is sitting in the row for T/O and Landing. If however the exit is manned by crew then you only need 1 pax per set of doors. The crew should have been moving at least one pax to the overwing so that all 4 "self Help" exits were manned. Had i have been a pax on the flight, I would not have hesitated to just go and sit there once the crew started to secure the cabin. Any BMI safety trainers wish to comment?