excellent suggestion from Erin , Gatwick Airport is pretty much en route and has good train links to Central London ( Gatwick Express is 15 mins but a bit expensive), you can get the concierge parking service , they have offices near the train terminal and it's much cheaper than the short term car parks and is secure. I've used them a lot and they are a really good service. Gatwick also makes is easy if you are coming out of london on the train and then picking up your car to drive to the South coast , it's 30 mins to the M3 , M4 or M5.
Don't forget to visit Devon if you are over here !!!!