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Transport Minister Steven Joyce ignored expert advice to cut the drink-drive limit and save lives after pointed questions from the Prime Minister's office suggesting there might be a public backlash.

John Key's office wrote directly to officials in the Ministry of Transport to ask if proposed changes to the limit meant "one glass of wine could put a person over the limit".

The concern, outlined in papers released under the Official Information Act, reveals fears that the public would react badly to a cut in the drink-drive limit - even though research and polls show most drivers are keen to see the limit reduced.

More than 8000 people have joined the Herald on Sunday Two Drinks Max campaign, promising to not drive after more than two standard alcoholic drinks.

But Joyce is refusing to cut the limit, saying more research is needed - despite his advisers telling him the delay will cost more lives.

His refusal came after John Hay, a prime ministerial policy adviser, sent officials a newspaper story from Britain where a similar debate is taking place.

The report included the claim that a limit cut from 80mg of alcohol per 100ml of blood to 50mg would mean some people could have only a glass of wine or pint of beer.

Hay said he needed a briefing so he could inform Key "as it is an issue he is concerned about". In a separate email, Hay also asked if officials had considered harsher penalties on people who had broken the existing limit of 80mg.

Officials told Key's office that the number of drinks a driver could legally consume before driving depended on a driver's height and weight. But they said a reduced limit would still mean someone of average size and build could legally have two drinks in the first hour and one drink each hour thereafter.

A senior official warned: "Drivers with a blood-alcohol content of [80mg], who are legally entitled to drive, are significantly impaired."