A POLICE estimate that a third more drivers will be prosecuted this Christmas as a result of the lowering of the drink-drive limit has been challenged by the Justice Secretary.

Kenny MacAskill told MSPs that evidence from other countries was more optimistic in terms of driver behaviour falling in line with a reduced limit from 80mg to 50mg per 100ml of blood on December 5.

The drink-driving limit will be reduced, backed by a widespread public awareness campaign to alert Christmas revellers. Police estimate they are likely to catch around a third more drink-drivers, Chief Superintendent Iain Murray told MSPs last week.

But Mr MacAskill told Holyrood's Justice Committee the police estimate was an "extrapolation from the raw statistics", and evidence from Ireland showed convictions fell after they reduced the limit in 2011.

He said: "Although the stats provided by Chief Supt Murray are correct, equally the practical delivery of this from Ireland (shows) it went down because it drove home a message to people: Don't drink and drive."

Conservative MSP Margaret Mitchell said: "So you're really dismissing this third that was given in evidence?"

Mr MacAskill said: "I'm not dismissing it. I'm referring to the clear statistical parallel from the Republic of Ireland when they did the same change that we propose to do.

"Their perceived wisdom would have been that more people would be caught because more people would have been 50mg and beyond, but in reality fewer people were caught because more people adhered to the law and didn't risk it. So it's extrapolation from the raw statistics."