Research commissioned by road safety charity Brake found that just 62% of motorists aged between 25 and 34 always wear a seat belt in a car.
The second-worst culprits are 18 to 24-year-olds, with only 71% saying they always belt up.
This is well below the 96% of drivers aged 55 and older who say they wear a seat belt without fail when in a car.
For 45 to 54-year-olds, the figure stands at 94%, while 74% of 35 to 44-year-olds stick to the seat belt law.
Brake said young people are often “more willing to take risks on the road”, which could be why they’re not always belting up.
The poll shows that while some people forget to put their seat belt on, in some cases they deliberately choose not to wear one.
Men are more likely than women to break the law, with 0.2% of women saying they never put their seat belt on, compared with 1.4% of men.
Wearing a seat belt has been compulsory for drivers and front seat passengers on UK roads since 1983, and for back seat passengers since 1991.
The punishment for not wearing one is a £100 fine, rising to £500 for cases taken to court.
More than one in five car occupants killed in recent years were not wearing a seat belt, according to Department for Transport figures.
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Brake’s head of campaigns Jason Wakeford said: “Research shows that younger drivers and passengers are generally more willing to take risks on the road, including actively choosing not to wear a seat belt.
“Also, younger drivers are more likely to believe they have heightened protection from vehicle safety features, like air bags and ABS (anti-lock braking systems), meaning they can take more risks behind the wheel.
“It is tragic that, despite these major technological advances, it remains the case that people continue to die or be catastrophically injured because some of us are still not using the most basic and vital vehicle safety feature of all – seat belts.”
The survey, which polled 2,004 drivers, also found that 12% of car passengers admit they wouldn’t speak out if the driver was speeding – with male passengers twice as likely as female passengers to keep quiet.
Furthermore, a quarter of drivers say they have knowingly driven the morning after drinking, even though they may still be over the limit.
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