An update: Car retrieval worked quite well. You MUST validate your ticket in one of the machines in the arrivals hall BEFORE you exit customs. Leave cases with travelling companion and leg it to the car. Find car and return to short stay carpark in front of terminal to collect cases and shivering Mrs.
We were lucky to arrive while there was a bit of daylight left - even with a few hundred new cars parked on what was an empty field when we left, I spotted our car without too much trouble. (Just to recap - you are parking in a field - there are no 'lane' markings - the rows are set up in an ad-hoc basis by the customers!) Our friends, returning in darkness the next day, had to stumble about in pitch darkness 'blipping' his key fob to get his car to flash his indicators at him.
He reported that there were a large number of people on a similar errand and were none too pleased with these arrangements. A lot of them had dragged their cases with them along the gravel road and damp meadow, then were having to go up and down the rows to find their car.
Tying an orange Sainsburys bag to the aerial when you leave the car may assist in finding it when you return (in daylight, ofcourse!).