On a recent A320 flight (non UK but EU airline) I saw 2 huge (I mean fat) men seated next to an overwing exit on a full 180 pax flight - No way could these guys try to exit the aperture in a hurry - they could barely breathe, puffing and wheezing, they were so overweight.
I looked at the hostie and she just shrugged...She was rather too busy trying to shove into the overhead lockers the 150 or so wheelie cases and cabin bags that had been brought on board...
I then looked over and saw a 70 to 80 year old couple, 'Mr and Mrs Nice' who were seated by the opposite exit.
The hostie just pointed at the seat placard notice showing them how to open, and then lift out a 20 kgs exit window and what to do with it...
Mr & Mrs Nice looked blankly at it...
shudder.