Around five million drivers believe they have got behind the wheel while over the drink-drive limit at least once in the past year, according to new research.
Some 16% of motorists think they have driven under the influence either immediately after consuming alcohol or the morning after a late-night drinking session, an RAC survey found.
The study found Londoners are the most likely to drive while over the limit, with fewer than three in four (74%) claiming they have not done this.
Police forces actively target drink-drivers in December. Department for Transport figures show 143 people were killed in collisions involving a driver impaired by alcohol last year.
RAC road safety spokesman Pete Williams said: "Anyone who thinks they are likely to have sobered up enough to drive just because they went to bed for a few hours may just be about to ruin someone else's Christmas as well as their own.
"If you are having to think whether you are sober enough to drive then the answer is you probably aren't.
"The dangers of drink-driving are truly horrific and should never be underestimated."
Some 1,727 motorists were questioned by the RAC.
The Scottish Government slashed the alcohol limit for drivers from 80 milligrammes (mg) per 100 millilitres of blood to 50mg in December 2014, but the legal level in the rest of Britain remains 80mg.