The Gatwick Express has not been operating whilst the airport has been closed. That makes some sense as there are no passengers, but there are still people who have to travel to/from the airport and surrounding area, so perhaps a substantially reduced service would have made sense.
Yesterday the other rail services were severely disrupted, today apparently there there were none and it took a friend of mine almost 5 hours to get to Victoria. All this disruption does seem excessive given the relatively small amount of snowfall, and that other countries with similar climates, e.g. Holland, do not seem to have been disrupted to anything approaching the same extent. The excuse that this is 'exceptional' is wearing a bit thin.