If you’re heading for London and have a Wednesday arrival, you can expect some delays and hassles, especially at Heathrow.
Various unions and labor groups have called an all-day “work stoppage” to protest austerity measures, and those stoppages will probably include customs and immigration officials and maybe rail and bus service. Some airlines are already waiving rebooking fees.
Check with your airline about possible cancellations and rebooking. Here are a few links to relevant service information from some of the major carriers to the U.K.: