The Scottish Government has had to abandon its aim of passing key drink-drive legislation in August after Home Office experts were two weeks late in completing the crucial type approval process needed to clear breathalysers for use at the new lower limit.
The Scottish Parliament met for the final time before the independence referendum last Thursday and MSPs will not return to the chamber until late September.
The delay has put a squeeze on the Scottish Government's aim of enforcing the new European-style limit of 50mg of alcohol per 100ml of blood, instead of 80mg at present, in time for this year's festive season, when rates of drink-driving typically rise.
A pint or a glass of wine could push motorists over the legal limit under the change, which will bring Scotland into line with Germany, France and Spain. It is predicted to save up to 17 lives a year.
Although Holyrood has the power to set drink-drive limits for Scotland, type approval - which verifies the accuracy of breathalyser readings to ensure they are admissible in court - is reserved to Westminster.
In a letter to Home Office minister Damien Green on January 7 this year, Justice Minister Kenny MacAskill stressed that type approval work had to be completed "by the end of July" to allow the lower limit to be in force in time for the 2014 festive season.
The Home Office had originally set a deadline of the end of September, but agreed to bring it forward two months after Mr MacAskill insisted that this would leave "insufficient time to complete all necessary preparatory and implementation steps, including recalibration of all evidential devices operated by Police Scotland and the parliamentary passage of the draft regulations required to effect the change".
However, the work - which cost the Scottish Government £25,000 - was not completed until August 15.
As a result, there was not enough time to pass the order before parliament broke up. The Scottish Government hopes to bring it before MSPs in late September or October, but it is unclear whether the revised timescale will leave enough time to roll out the new limit for Christmas.
The latest glitch comes after complaints that Whitehall's work on developing roadside "drugalysers" for use in England and Wales was being prioritised over the type approval process, although the Home Office denies this.
MSPs voted overwhelmingly in November 2012 to cut the drink-drive limit, and the Scottish Government initially hoped to introduce it in summer 2013.
A Police Scotland spokesman confirmed work is underway to recalibrate breathalysers.
Neil Greig, Scotland-based policy director for the Institute of Advanced Motoring, said: "We are very pleased to hear that finally progress is being made on this issue, although it is disappointing to hear that the latest delays mean the limit might not be in place for Christmas. It was ridiculous that a well-supported law in Scotland was held up purely because of a civil service backlog in London.
"The new law promises to save between three and 17 lives a year. If it works in Scotland it will almost certainly lead to pressure for England to follow suit or be out of step with the majority of countries across Europe."
A spokeswoman for the Scottish Government said: "Lowering the drink-drive limit will bring Scotland in line with most other European nations and save lives. The Scottish Government is working to bring in the lower drink drive limit as soon as possible."