The proposal will effectively toughen the law, reducing the amount of drink that drivers are allowed before they are over the legal limit. But it will also allow some of those convicted to escape a ban as long as they have not exceeded the second, higher limit.
Precise measures are impossible to give, but the new limit will restrict drivers to roughly one pint of beer or two glasses of wine. The change is almost certain to lead to confusion as drivers try to keep track of how many drinks put them over the first limit, punishable by a fine, and how many more will lead to an automatic driving ban.
The move will be highlighted in the Government's consultation document on drink driving, which will be launched by the Department of the Environment, Transport and the Regions (DETR) tomorrow. Ministerial sources said that the two-tier scheme is now the Government's firm favourite.
Although a period of consultation will follow, Whitehall expects the new system to become law rapidly thereafter, bringing Britain into line with most of the rest of Europe. The UK is out of step with many other European countries in not having a graduated system of drink-driving offences, although magistrates do have guidelines for imposing jail sentences on serious and repeat offenders.
The planned change in the law comes after pressure from Neil Kinnock, the EU Transport Commissioner, to reduce the blood alcohol limit to 50mg of alcohol per 100ml of blood, down from the present 80mg limit.
The reduction, proposed as part of a new EU directive, has been blocked by several countries, including Britain - although the Government's formal position is that it is "studying" the plans. The UK's opposition is now crumbling, with the two-tier system seen as the easiest and most sensible solution.
Under the new plans there would be reduced punishments for those caught with between 50mg and 80mg of alcohol per 100ml. The penalties are likely to involve fines but fall short of the automatic one-year ban which drivers can expect if they stray over the current 80mg limit.
Motoring organisations are likely to oppose the move, calling instead for tougher policing of the existing law. But the change would also bring many more motorists within the scope of the drink-driving net. Random breath-testing by the DETR revealed that 2.3 per cent of drivers could be driving with alcohol levels of between 40mg and 80mg.
Drink-related road deaths have halved since the introduction of breathalyser testing in 1967. This is due in great part to society's increasing intolerance of drink driving.
The year before Barbara Castle introduced breath tests, 7,985 people were killed in road accidents. Thirty years later the figure has more than halved to 3,598, despite a huge increase in the number of cars on the road.
France, which has twice as many fatal road accidents as Britain, lowered its limit to 50mg in 1995 and introduced campaigns to inform people how much they could drink. Disposable breathalysers went on sale in service stations, supermarkets and chemists. First indications show that lives have been saved.
Sweden has Europe's lowest level, set at 20mg per 100ml.Reuse content