There was a furore recently, at Gatwick and other UK airports, about valet parking companies that were doing just that - picking up your car from you at the terminal and then leaving it in a random residential street.
http://www.dailymail.co.uk/news/art...nies-Heathrow-Gatwick-Manchester-exposed.html
Those are the off-site companies, the official on-site companies park in the terminal car parks in designated secure zones