If you want to see excessive luggage then all you have to o is take a flight to West Africa. My usual trip to Accra can be a nightmare, the gate staff are usually pretty good at combing the gate area for large bags and gate checking them.
In some ways this annoys me as all the regular travellers know this so are basically just adding to their baggage allowance free of charge.
The worst excess I have witnessed was a few years ago (not on BA) where the airline manager came up to me to apologise the delayed departure telling me that the final passenger had finally arrived at the gate with 2 large suitcases and 16 bags from Duty Free. He then proceeded to scream at the gate staff when he was told he would not be taking that lot onto the aircraft. The end was very sweet as the airline were already searching for his baggage in the hold, it was found before he finished screaming so he was removed from the flight!