Gatwick Airport (LGW) Overview...
The Gatwick airport is located over 40km away from the main central areas of London. The airport, which handles a fair amount of intercontinental flights, is reasonably comfortable. The facilities are what you'd expect from a large European airport, and most of the shops are nicely tucked away - yet easily accessible if you want them.
The bad news is that the airport is an absolute minimum of 3 hours away by train - meaning you're likely to have to allow 4 hours or more to safely get to the airport (we always recommend you schedule your transport to arrive in plenty of spare time for the check-in to your flight).
Note Gatwick is split into two terminals - North and South - and it's certainly worth finding out what terminal you're departing from before you get there. Coach operators will usually offer to drop you off and pick you up at either Terminal (make sure you book from the specific Terminal so the driver is expecting you). Travellers arriving by train arrive just a few minutes (covered, inside) walk from the South Terminal. Add another 5 to 10 minutes to reach the North Terminal, which is connected to the South Terminal by a rail transit link