Originally Posted by
stut
If you want to get the National Express coach, and leave 2h before departure at Gatwick, you'll need to be at Heathrow bus station at 04:05. That's a 3am alarm call.
And this in itself will cause you a problem as you won't be able to easily get from the hotel to the central bus terminal at that time.
If you're coming from central London, I'd be tempted to write off the cost of the hotel and go to Gatwick instead. You could always call the hotel up & explain - worst they can say is no, but they might let you transfer the booking to a HI at Gatwick?