On average, it takes about one hour for your body to break down one unit of alcohol. However, this can vary, depending on your weight, gender and age.
If you drink a large (250ml) glass of wine, your body takes about three hours to break down the alcohol. A pint of beer takes two hours to break it down, while one pint of strong lager is equivalent to three units, so this will take longer.
If you have a few drinks during a night out, it can take many hours for the alcohol to leave your body. The alcohol could still be in your blood the next day.
This means that if you drive the day after an evening of drinking, you could be over the legal alcohol limit.