My wife was caught up in the LGW fubar on Christmas Eve - having had a BA domestic cancelled mid morning (due to depart circa 6pm) and her subsequently booked Easyjet replacement flight also cancelled around 2pm (she went to airport early from work via a taxi with the public transport issues)
Without labouring the points made, her view was that front line staff were simply not being fed the information they needed to advise pax. For example her flight was showing on the excellent EZY app as cancelled - however LGW staff refused to let her go back land-side (via escort) as far as they were concerned the flight Wasn't cancelled!
She did comment that throughout the front line staff did exceptionally well to maintain a level of customer service (Calm, considered etc) whilst under extraordinary pressure. She did have sympathy for them despite her situation (which to be fair was no where near as bad as some other people).
She eventually 'escaped' and travelled north via hire car.