I was able to get a great deal to fly home (back to US) from London Heathrow on Christmas Day (2009). It never occurred to me that public transport would be closed, but I read on another board that it is. Does anyone know exactly what they mean by "public"? Buses, tube, trains to airport, cabs? Any helo would be gladly accepted.
Buses, trains and the underground don't run on Christmas day - the only exceptions are the Gatwick and Heathrow express trains which run a limited service.
Taxis do work on the 25th although they can be hard to come by as a lot of cabbies take the day off - best to book in advance rather than trying to pick one up on the street.
Try Easybus and see if they run on Christmas. They have an inexpensive bus from London to the airport.
Can you arrange transport to Paddington station? Friend or taxi, maybe? Then take the train to Heathrow.