According to a poll by YouGov and the Society of Manufacturers and Traders (SMMT), 43% of motorists have left their keys with people they do not know at garages, hotels or airport parking.
It comes as official figures show that vehicle thefts have spiked in recent years, with around 80,000 cars stolen between March 2015 and March 2016.
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Experts have warned that a large portion of these could be due to criminals making copies of key fobs that provide electronic access to cars.
Using high-tech equipment, gangs can hack into security systems, capture key data and then steal a vehicle at a time when they know the owner will not be around.
Earlier this year, motorists were advised to leave their vehicle in a secure location and invest in steering locks to counter the rise of car thefts.
It was thought that luxury cars including BMWs, Range Rovers and Land Rover were among the most commonly targetted by tech-savvy thieves.
Drivers are now being warned to take steps to ensure their vehicle is safe and secure after parking.
The SMMT report said: “Investment in new technology means that all new cars sold in the UK now have an immobiliser and many are fitted with an alarm and double locking as standard.
“Car owners can also play an important part in protecting their vehicles by taking simple preventative measures, including parking in well-lit and secure parking spaces, double checking your car is locked before walking away, and checking the credentials of any company with which you leave your keys.”
In the survey, which had more than 2,000 respondents, 71% of people said they did not make sure that a company or individual followed an accredited code of practice before handing over their keys.
Many participants in the research also said they often made the mistake of leaving car keys close to the front door where they could easily be seen by thieves.
By contrast, just 11% of those polled said they would trust a stranger with their house keys.