Half of Britain's drivers and motorcyclists admit to drinking before driving, a survey has suggested.
Many people have a poor grasp of alcohol units and the law
One in three said they had driven after drinking two units of alcohol, and 10% had driven after drinking three.
One in 10 motorists admitted to drink-driving once a month or more often.
The survey, by road safety charity Brake for Green Flag Motoring Assistance, comes as the Christmas anti-drink drive campaign begins.
This year, the government is re-running a TV advert used earlier this year, showing a young female cyclist being involved in a crash
with a drink-driver.
In the Brake survey, a quarter admitted to drink-driving even when they knew the alcohol was affecting
And 28% said that they had risked driving first thing in the morning after
drinking a lot of alcohol the night before.
The survey also showed that motorists had a poor grasp of alcohol units and the law.
Standard (175ml) glass of wine - 2 units
Large (250ml) glass of wine - 3 units
Pint of standard lager - 2.3 units
Pint of premium lager - 2.8 units
Pint of strong cider - 4.7 units
The legal drink-drive limit is 80mg per 100 millilitres of blood, but this cannot easily be translated into alcohol units as it can be affected by build, sex, whether food has been eaten, and a host of other factors.
Half of those questioned mistakenly thought that two 25 ml shots of vodka were more alcoholic than a pint of 5.8%-strength lager.
The real answer is that the lager is about three units, while the vodka is about two units.
Just over half wrongly thought it would take two or more units to affect their driving, while 8% reckoned it would take four or more units.
The real answer is that any amount of alcohol affects driving ability, and there is no safe limit.
Many thought there was a relatively small chance of being caught drinking and driving.
Brake's chief executive Mary Williams said: "The war against drink-drivers
has not been won. The findings highlight a lethal ignorance of drink-drive law
and the effects of drink driving, and widespread levels of drink-driving.
"Drivers should never drink and drive - not even one."
Drink-drive deaths have fallen dramatically over the last 20 years, but have been edging up recently. There were an estimated 560 deaths in the UK last year - 6% more than in 2001.
It is no longer accurate to say one glass of wine is 1 unit
A large glass could easily be 3.25 units
A pint of strong 8% lager could easily be 4.5 units
Road Safety Minister David Jamieson said: "Drink-drivers are still
"If you are going out and enjoying yourself over Christmas, don't turn your
night into a nightmare.
"Leave the car at home and, if you can't use public
transport, designate a non-drinking driver. Remember that you could still be
over the limit in the morning after a good night out."
The AA Motoring Trust called for similar campaigns all year round.
A spokesman said: "People know that drink-driving is an enforcement target at
Christmas, but may not believe it is at other times of the year."
A Green Flag spokesman said: "Most drivers do behave responsibly and make other transport arrangements if
they know they are going to drink, but there is still the hardcore who think
they can take the risks that ultimately could end theirs or someone else's