Christmas party season is upon us. A time for celebration, a time to be festive and merry and eat and drink lots. But its also unfortunately a time when people choose to drive after one too many at Christmas celebrations and for some this can have catastrophic consequences.

As motoring solicitors a question we are frequently asked is how much alcohol is safe to drink before driving.

What is the drink driving limit?

The drink driving limit differs depending on whether you are in England, Wales, Northern Ireland or Scotland.

The limit in England and Wales is 80 milligrammes of alcohol per 100 mls of blood. This equates to 35 micrograms per 100 mls of breath or if a urine sample is given the limit is 107 milligrammes of alcohol per 100 mls of urine.

In Scotland the alcohol limits are lower and are 50 milligrammes of alcohol per 100 mls of blood. The breath limit is 22 micrograms of alcohol per 100 mls of breath or 67 milligrammes per 100 mls of urine.

How many units of alcohol are in a glass of wine or a pint of beer?

The size and strength of your drink is determined by the number of units that you are drinking. As an example, wine comes in different strengths and different sizes. There are generally three different pub measures of wine being a small glass (125 mls), a medium glass (175 mls) and a large glass (250 mls).

Wine also comes in different strengths ranging generally between 11% ABV and 14% ABV.  Therefore there can be a significant difference between the number of units of alcohol in a glass of wine. A small glass of 11% wine might only contain 1.4 units whereas a large glass of 14% wine may contain 3.5 units.

Similarly lager and beer come in different strengths and the strength of the lager will affect the number of units of alcohol contained within it. A pint of strong lager could contain more than 3 units of alcohol.

How much alcohol can you drink before driving?

It is not possible to accurately determine how many units of alcohol one can consume before driving as you cannot easily convert the drink drive limit into units of alcohol. 

There are a number of different factors that can impact how alcohol is absorbed into your blood which can place you over the drink drive limit.

Such factors can include:

  • Your weight
  • Your age
  • Your sex
  • Your metabolic rate
  • The type of alcohol you are drinking
  • The amount of alcohol you are drinking
  • What food you have eaten
  • Any medical issues you have
  • Any medication you may be taking

It could take two hours for a pint of lager to leave your system and potentially even four hours for a large glass of wine to leave your system. In addition to the amount of time for the alcohol to leave your system you also need to allow time for the alcohol to be absorbed into the system.

It is too difficult to predict how long it would take after having consumed alcohol for you to be under the drink drive limit due to the individual factors that contribute to how your body processes alcohol.

The easiest way to avoid being over the drink driving limit is to not drive when you are drinking alcohol and to have ‘none for the road’.

What about driving the ‘morning after’?

After a heavy night out it is crucial to consider how this may affect you. At Olliers Motor Law we deal with many clients who have been stopped whilst driving ‘the morning after’ a night of drinking alcohol. Again, as everybody deals with alcohol differently and processes alcohol at different timescales, it is impossible to say when you will be safe to drive the next day if you have had a heavy night. If you are going to be consuming a large amount of alcohol during an evening we would always suggest that you do not drive the next day and enjoy the opportunity to relax instead.

There is a calculator available at to enable you to calculate when it may be safe for you to drive the morning after drinking alcohol. It can also help you calculate when to stop drinking alcohol if you have to drive the following morning. However we would stress that this should be used as a guide as opposed to  a definitive, conclusive result.

Ruth Peters – specialist motoring lawyer

Written by Ruth Peters, specialist motoring lawyer at Olliers Motor Law. If you require further advice in relation to an offence of drink driving (or indeed any other motoring offence) please contact Ruth on 0808 168 0017 or 07714 680535. You can also email Ruth at [email protected] or click here to contact us.

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