Our insurance is there to pay out if we have an accident or our car is stolen – so it's particularly worrying to discover that potentially millions of drivers are making a mistake that would leave them with no cover at all if someone drives off with their car.
Worse, anyone trying to appeal their insurer's decision not to pay out in the event of theft is likely to be given no slack from the official watchdog either – according to a warning from BP Insurance Brokers.
The mistake? Leaving your keys or fob in the car while nipping out to drop something off or pick something up.
"The easiest way for a thief to steal a vehicle is to prey on drivers who make this mistake. Despite this, relatively few drivers always take their keys when the car is unlocked," the high street insurance broker warned.
And in many cases, you'll be doing this in precisely the worst places too.
"Thieves are aware of 'key places' where they could find keys in the ignition, including locations near cash machines and postboxes and outside shops into which drivers might 'nip' to pick something up, or deliver it," BP warned.
"Many motorists leave cars unlocked on the garage forecourt and also frequently leave the key in the ignition on their own driveway, or outside their house. The latter often occurs in winter, whilst drivers are waiting for their car windows to defrost, but is also frequently the result of being distracted by something else when arriving home, whether that is getting a child out of a car seat or unloading the shopping."
So what should you do? The advice is simple – if not always the easiest to follow: Always lock an unattended car as soon as you leave it.
"Motorists need to be extremely vigilant and make sure they do not accidentally leave their car keys in the ignition, or walk away from an unlocked vehicle that can quickly be accessed by a car thief and driven away," Barry Pimlott, BP Insurance Brokers' managing director, said.
"They should also not place their trust in anyone they do not know well, by handing over their keys. Finally, they should ensure they do not leave their car keys in a place from which they could be stolen by someone breaking a window, or hooking them through a letterbox.
"This really does happen, so keep your keys somewhere very safe and out of both view and reach."