How long after drinking can you drive again?
28 November 2013 Last updated at 16:24 GMT
The number of motorists arrested for drink-driving the "morning after" has risen, police figures suggest.
It comes after insurers LV found that many motorists do not realise how long it takes for alcohol to leave the body.
Roger Singer is Head of Drink Driver Education a drug and alcohol road safety charity that runs training courses for people who have been caught breaking the law.
He told BBC Radio 5 live's Breakfast that the best way to work out whether you are fit to drive is by counting up the units of alcohol "then counting them down one unit per hour."