Contrary to Duggies evident belief lots of BA employees work over Christmas, not just cabin crew. The prospect of spending the day somewhere sunny with the family in tow on a free duty ticket is probably quite exciting for them. I'd imagine they'd also do something more downroute than sitting in their rooms sulking that they've had to work, which is what most of the crew have done on the Christmas trips I've worked.
And by the way, every department in BA has finished this round of negotiations with the Leadership Team with the exception of Duggies.