New drink-drive limit is simply a safety margin

The IAM supports this change as a positive move to reduce casualties; a significant number of crashes involve drivers who are between the old and the new limits.

However, a lower limit can still imply that there is some safe amount we can drink before driving. When the 80mg limit was introduced in 1966, the UK Government was very reluctant to publish any figures about how much alcohol was “safe”, so rumour took over – a pint and a half was fine, or maybe it was two pints, but you could have a bit more if you had a meal as well . . . in other words, myth and misinformation rushed in to replace fact.

This time we must all be clear about what the limit means. The 50mg level does not mean you can still have a bit to drink and be safe to drive. It is simply a safety margin for the residual amount of alcohol you might still have in your body if you drive the day after having a few drinks – not a binge session, just a few sociable drinks.

Our livers break down alcohol at an average rate of one unit per hour. Drinking three pints of beer (about 6 units of alcohol) on Tuesday night can easily result in one unit or more still being present in your body on Wednesday morning – roughly 15-30mg per 100ml. It is not practical to make the blood alcohol limit zero, but the new rule effectively says that there is no “safe” level of drinking and driving.

The message is clear and simple. If you have a drink, don’t drive. If you are going to drive, don’t drink.

• Tim Shallcross is head of technical policy and advice at IAM Policy and Research