and the measure is on the departure time from Gatwick - not arrival, so the block time on the flight ex Gatwick is irrelevant.
Airlines in general are increasing block times because: A) there is growing congestion on the ground - so longer taxiing times b) there is more congestion in the air - so longer flying times c) EU261 requires carriers to pay compensation for late arrivals even when causes are outside of their reasonable economic control. So if a 15 minute longer published flying time means passengers arrive on a late flight less than three hours after scheduled arrival time, there is a huge saving for the carrier. So if you are a carrier that doesn't have a particularly high utilisation programme, you might as well make your scheduled times as long as you can. One of the effects of this ludicrous piece of legislation!