I used Gatwick last year and it took nearly three hours by car to get to Heathrow to catch a flight. National Express I used about four years ago, on the return trip after a flight inbound via Heathrow not one of their scheduled coaches stopped, there was nobody to ask to get information and even though I had given myself over four hours to get to Gatwick we missed our flight back to Guernsey, on that particular trip I had no choice but to fork out over £300 for the two of us to use Flybe on a one way flight back into Guernsey. I complained to National Express along with about half a dozen other passengers who had suffered the same fate and I never even got a reply. I find it cheaper to use a taxi. As I said, I've given up using London airports when I can.