Drivers have been warned they could be invalidating their car insurance this Christmas without realising it by participating in a common road practice.
It comes after new research revealed many motorists wrongly believe their fully comprehensive car insurance allows them to drive any car.
A survey found more than a third of drivers think they are automatically covered by insurance when driving other people's cars.
The study revealed 37 per cent of people who volunteer to be designated drivers believe they are legally insured to drive any vehicle.
In the past, many comprehensive insurance policies included a "driving other cars" rule as standard, with drivers not needing to double-check this.
But today, the feature is often removed unless drivers specifically ask for it, meaning Britons could unknowingly be driving illegally.
In the UK, anyone caught driving without proper insurance faces an immediate £300 fine and six points on their driving licence.
Chris Bibby, chief executive of Dayinsure, warned drivers not to make assumptions. He said it is illegal to drive any vehicle without at least third-party insurance. Even if the car itself is insured, the driver must also be insured to drive it.
Anyone caught driving without proper insurance faces an immediate £300 fine
| GETTYIf the case goes to court, the punishment can be even tougher with drivers facing much higher fines, more penalty points, and even risk losing their licence.
In serious cases, police can seize the vehicle which can leave both the driver and the car's owner struggling to get home and facing further costs.
The research also showed how common designated driving has become. Nearly half of people in the UK said they have acted as a designated driver for a Christmas party or festive event in the last three years. Despite this, many people are still failing to check their cover before offering to drive.
The survey found two per cent of drivers rarely check their insurance status at all while another six per cent said they only check occasionally.
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The rising cost and inconvenience of taxis may be part of the problem. Around eight out of 10 partygoers revealed they spent up to £50 getting home after a night out in December.
Long waiting times are also common, with almost one in 10 people saying they have waited up to an hour for a taxi to arrive.
These problems make driving a friend's car seem like an easy and cheaper option. However, it could turn out to be a very expensive mistake.
Experts warned that drivers may not be covered by insurance policies in other vehicles
| GETTYDrivers have now been urged to carefully check their insurance policy before getting behind the wheel of another vehicle.
Mr Bibby said: "Millions of people will act as designated drivers this Christmas. While the intention is good, drivers must check their insurance properly to make sure they are legally allowed to drive friends, family and colleagues' homes."
Even where the cover exists, there can be limits. Drivers under 25 are often excluded. Others may only have third-party cover, which means any damage to the borrowed car would not be covered.
To help compensate for this issue, experts suggested using short-term insurance as one option for those unsure, with cover available from as little as one hour up to 30 days.