I used one of these park and fly companies last year at Gatwick, and I was suprised how good they were. Just turn up, park in the que, book in and go on holiday. When you come back you board the bus at the terminal, get to the pick up point for your car, and as if by magic, its at the front of the que for you to get in and away.
Simple. I was as I say impressed.
Doing the same this year.