Road safety campaigners welcomed the announcement by Justice Secretary Kenny McAskill in March that the limit in Scotland would be cut from 80mg per 100ml of blood to 50mg. The expectation was to bring Scotland into line with mainland Europe as early as next year.
The change, which would make it illegal to get behind the wheel after consuming less than a pint of lager, is expected to save around 17 lives a year on Scotland's roads.
But the move risks being delayed until as late as 2015 because Home Office experts who are essential to recalibrate the testing equipment have been diverted into producing "drugalysers" for use on motorists in England and Wales.
It is understood that the Scottish Government has become increasingly frustrated about delays in recalibrating the equipment, which must be done before police can legally stop and check drivers against the new lower alcohol limit.
Although the Scottish Government has the power to set its drink-drive limits, the process required to ensure all the breath test devices used by police are uniform and accurate at the new limit is reserved to Westminster. But this process has apparently been held up while work on new drug-drive testing kits for use on motorists south of the Border is given priority by the Coalition Government. The Home Office denies this has caused the delay.
Neil Greig, director of policy for the Institute of Advanced Motoring, said: "Legislation as important as this shouldn't be held up by what is essentially an administrative procedure. Obviously the equipment needs to be accurate, but it shouldn't be this difficult to get it ready.
"This is an extremely popular and widely supported change in the law which should be implemented as soon as possible."
A public consultation on reducing the drink-drive limit in Scotland was backed by 74% of respondents, as well as having the support of three-quarters of MSPs. Figures published last week estimated that 680 road casualties in Scotland in 2011 - of whom 20 died -were the result of drink-drive crashes.
Margaret Dekker, secretary for Scottish Campaign against Irresponsible Driving (SCID), said control over recalibrating breath testing equipment should be handed to Holyrood.
She added: "I don't understand why that power can't be given to the Scottish Government as well because we have Police Scotland now and it's up to the police to enforce this, isn't it?
"It should be possible to calibrate the equipment in Scotland as well as setting the limits.
"This is Westminster dragging its heels again. The 50mg limit is already widely used in Europe and I assume their equipment has been calibrated, so I really can't believe there needs to be such a delay. This will cost lives. Drink driving is a serious issue, and this is simply unacceptable."
A spokeswoman for the Scottish Government said: "The Scottish Government has made clear our plans to lower the drink-drive limit in Scotland as this will help save lives and make our roads safer. We are working with Police Scotland and the UK Government to prepare for a lower limit, including obtaining the necessary type approvals for the devices used by the police to test drivers.
"A lower limit cannot be brought in until the necessary approvals are obtained through the UK Government, and we have made clear to the UK Government that we view introducing a lower limit in Scotland as a key priority. We expect the UK Government will prioritise this important work in line with the wishes of the people of Scotland."
A spokesman for the Home Office said: "Our work on roadside drug testing devices is not responsible for any delay to the Scottish Government's plans to reduce the country's drink-drive limit. Our advisers are in continuing discussions with Scottish colleagues to ensure devices used to enforce any new limit in Scotland are suitable for that purpose."