We had a very similar experience to this on the UVF to LGW route about two months ago (March). Mrs Prof and I were both booked in CW (and GCH) but had our seats jumped around from choice to something else twice as aircraft were changed back and forth in the week before the flight. When it came to the day, we stayed in CW, but many people were downgraded and not happy, to the extent that the Captain made an announcement to the effect that he appreciated that there was discontent about many downgrades, but please to not take this out on the cabin staff as they could do nothing about this, and please direct complaints to BA direct. Maybe one of the main benefits of being a GCH is protection from downgrades.... ;-)