Do you know of a pub or restaurant that will be open on Christmas Day? We will be staying at a hotel but they only serve breakfast.
Check The Drayton Arms on Old Brompton Road
I have not eaten at this pub ... just found it when I was looking for options for Christmas last year (I did not end up going over Christmas).
Timeout magazine (available online only these days) is always the first reference to check for all things London.
Otherwise the day you arrive check out the neighborhood around your hotel. Many ethnic restaurants do not close.
Stop by the closest pub and ask if they'll be serving and if yes, reserve.
If you are walkers and want to start Christmas Day early you might consider walking over to the Serpentine in Hyde Park to watch the Peter Pan Cup race. Much fun. A bout a mile and a half depending on the location of your Earls Court hotel. http://www.visitlondon.com/things-to-do/event/10716901-peter-pan-cup#6vmzuazAV6gCx2Hq.97