Police claims that they expect to catch around a third more drink drivers when the alcohol limit is reduced on December 5 have been challenged.
The limit will be reduced from 80mg to 50mg per 100ml of blood, backed by a widespread public awareness campaign to alert Christmas revellers.
But the figure has been challenged by Justice Secretary Kenny MacAskill who said the projection is not supported by international evidence.
Chief Superintendent Iain Murray earlier said: “A quite significant campaign will be ratcheted up to make people aware of the implications.
“The worst-case scenario could be that as many as a third more drivers will be caught, but I would like to think that it will be less than that.”
But Mr MacAskill told Holyrood’s Justice Committee evidence from the Republic of Ireland shows convictions fell after they reduced the limit in 2011.
He said: “What Superintendent Murray has tried to do is simply work out those who were between 50mg and 80mg and therefore more likely to be caught.”