Young drivers are getting behind the wheel after a night out drinking without realising they are over the limit, new research suggests.
It can take some 12 hours to be safe to drive after four pints
Many are unaware of the time it takes alcohol to leave the body, a survey of 2,000 adults by Direct Line found.
The majority do not know it can take 12 hours to sober up after four pints of continental lager, the study says.
Road safety campaigners are urging drivers to heed the warning ahead of the Christmas party season.
The survey found that one in three motorists drive the morning after a heavy drinking session and that youngsters are the worst culprits.
Men think it will take seven hours to be completely safe to drive and younger drivers - 18 to 29-year-olds - believe they can drive after six hours.
However, the report states, medical research shows that it can take around 12 hours to be sober enough to drive after drinking four prints of continental lager or ale.
Direct Line spokeswoman Emma Holyer said: "Many people forget that they are still not sober enough to drive after having a night's sleep.
"The research shows the awareness among motorists is shockingly low towards the dangers of driving the morning after."
'Not a drop'
Caroline Chisholm, campaigns manager for road safety charity Brake, said: "The drink-drive message just isn't getting through to a whole generation of young drivers.
"It's very difficult to work out what you can have, and any amount of alcohol affects your driving. The only safe limit is not to drink and drive at all, not a drop.
"We want people to enjoy themselves this Christmas, but if you've been drinking you may still be over the limit the next morning.
"If you're planning a night out drinking, make sure you take the bus, train or a lift to work the next day."
The survey also found that in the last year more than half of male drivers drove within two hours of having a drink.