no explanation....

We were travelling back to Derbyshire after being home to Southport and had reached the Chatsworth area.We slowed down to negotiate a bend when a car backed out of a drive in front of us.We stopped about ten feet from it,relieved that we hadn't been speeding.Immediately,we both saw that there was no-one driving it.We were close enough to have a clear view of the interior and there was no-one in the driver's or the passenger's seat.We looked at each other in surprise and decided that we'd pull in and then warn the owner that his car had 'escaped',perhaps due to a faulty handbrake.Suddenly,the car began to move forward,back into the driveway,on it's own.As we passed the house we drove slowly past,expecting someone to get out of the vehicle.No-one did,and the car remained where it was,still driverless.We've been trying to think of an explanation without success.....