NOT the answer to your question, but I can tell you that the LHR T1 lounge was open last year on Christmas Day.
For the hour so my wife and I were there, staff outnumbered passengers (by 4 to 3 if I remember) and one kind BA lady circulated amongst us with champagne.
Add mince pies, empty airport (through security in about 3 seconds!) and it was a fine experience - except for the trek to 45/46 (? - at the end of the T1/T2 pier) where the only BA flights were waiting. Other stands had parked aircraft.
Good luck in T4!
[This message has been edited by Roger (edited Dec 18, 2003).]