Lord Adonis, the UK transport minister, yesterday finally bowed to mounting pressure from road safety groups by appointing an internationally renowned legal expert to come up with recommendations on a revised level.

Sir Peter North will examine proposals to reduce the legal alcohol limit from 80mg per 100ml of blood to 50mg, as well as exploring whether new legislation is required to crack down on drug-driving. He is due to present advice on both issues by the end of March 2010.

The move was welcomed last night by Scottish ministers, who have been pushing for a lower alcohol limit as part of a devolved road safety strategy and have called for powers on the issue -- which are currently reserved -- to be transferred to Holyrood.

However, the topic has become a potential UK election battleground, with the Tories reiterating their opposition to introducing lower penalties along with a lowered legal alcohol limit.

Theresa Villiers, the party’s shadow transport secretary, said: “We have yet to be convinced of the case for an across-the-board reduction in the drink-driving limit and would certainly strongly oppose any moves which would see the penalties for drink-driving reduced or a move away from the mandatory ban.”

Sir Peter, whose work has underpinned legislation covering traffic law and parades in Northern Ireland, said he would arrive at “independent” views on drink and drug-driving. “The legal and practical issues are not easy to resolve but I intend to consult widely on these matters,” he said.

His review will consider either lowering the limit for drink-driving or introducing a separate, lower limit that would not attract the same level of penalty. The likely effect on drivers’ behaviour will also be examined.

He is also expected to come up with recommendations on new offences that make it illegal to drive with named drugs in the system at specified levels, similar to the law in place for alcohol.

Lord Adonis said: “Road safety has improved significantly in recent years -- 1,000 fewer people now die on the roads in a year than in the mid-1990s -- and Britain now has one of the safest road systems in the world.

“But we need to cut further the number of tragedies on our roads. Drink-driving killed 430 people last year and research suggests drug-driving is a key concern for the public.”

Road safety groups and motoring organisations welcomed the announcement. Edmund King, president of the Automobile Association (AA), said: “We are pleased that these complex issues will be addressed. Sixty per cent of AA members have indicated that they would support a lower drink-drive limit, with 20% opposed. However, the legal issue is more complex than the limit as a sliding scale of penalties could reduce the deterrent effect.”

A spokeswoman for the Scottish Government said it was “ready to act now” following a report on road safety made last year by its own expert group.

“We continue to press the UK Government to act swiftly to implement the Calman Commission recommendations and to transfer these powers to Scotland,” she said.

“Our position is quite clear -- we want to see a reduction in the drink-driving limit and for the police to be given the power to carry out random breath tests at the side of the road. The current limit simply leaves too much room for confusion and sends out the wrong message.

“That’s why we need to have a lower limit, one that sends out a clear message that driving after you’ve had a drink isn’t acceptable -- it’s dangerous.”