British airports, especially Heathrow, have had massive delays and many cancelled flights due to fog. The standard advice is: Check with your airport.
This is Heathrow's official website. This website has a link to click to get to a number of the airports in the UK including Heathrow. (Click on the Heathrow Airport link). They say, "Check with your airline."
As of today, December 22, 2006, there are still lots of delays.
One thing you "might" try is to check with regional airports and see if you can get out from an alternate location.
