Originally Posted by
windowontheAside
I don't think that's the case. The US doesn't recognise 'transit' - they would have to enter the US which involves reclaiming their bags and clearing US customs before rechecking them for the connection.
No, there are some exceptions although you always have to do immigration (and the TSA have the 'right' to rifle through your bags anyway so they can find anything dodgy). I'm sure I've heard of it being applied at Houston as well.
To the OP - not sure if you can even cancel the car park booking but Alamo/National have quite a nifty arrangement whereby you can hire a car to drive to the airport. So long as you only have it for 24hrs, it's £55.
I guess you also need to be convenient for one of their locations in the first place.....
Or there's a reference here
http://www.holidayextras.co.uk/heath...3-parking.html to a firm that will move your car between Heathrow & Gatwick for you....