The Government has defended its decision to ignore official advice and delay lowering the drink-driving limit, despite Opposition claims that it could cost 60 lives.

Last month the Government announced it would wait for New Zealand-specific research over the next two years before deciding whether to lower the blood alcohol limit from 0.08 to 0.05 (50mg-80mg per litre of blood).

Papers obtained by NZPA under the Official Information Act showed lowering the limit was the best action to reduce the number of people killed by drunk drivers.

As NZPA reported in August, the Transport Ministry estimated reducing the level could save 33 lives, prevent up to 680 injuries, and save up to $238 million every year.

An email from a ministry employee said statistics showed people with a blood alcohol level between 0.08 and 0.05 caused 30 deaths between 2006-2008, and a Cabinet paper said keeping the same level would mean the goal of reducing the level of drink-driving fatalities to the Australian rate would not be met.

Prime Minister John Key said the officials' view had been known for some time but Cabinet had decided there needed to be more evidence about drivers with between 0.08 and 0.05 blood alcohol limit.

"There is holes in the information we have, we can't tell you exactly in terms of people between 0.05 and 0.08 unless the driver was killed at the scene we don't have that information because if you pass a breath test and you're 0.07, for instance, we don't record that data."

He said there was more likely to be a consensus after information was collected over the next two years.

Transport Minister Steven Joyce said the ministry's figure that 30 people a year would be saved if the blood alcohol limit was lowered was an estimate.

"It's effectively a projection of what they think will happen, can't be anymore accurate than that."

He said lowering the blood alcohol limit was an emotional and contentious issue that had been debated for years.

"There is a sizable body that want it to happen and there is a sizable body of people who are worried that they'll be criminalised for doing nothing more than having one or two drinks before they drive and they feel that they'd be quite safe in doing that."

Among the papers released today an email from a Transport Ministry staffer said continuing with the current limit would not see improvements in reducing alcohol related deaths and injuries.

"In other jurisdictions lowering the limit to 0.05 reduced the level of alcohol consumption across the population of drink drivers and achieved the ultimate objective of reducing the level of fatal crashes," the email said.

Labour leader Phil Goff said the Government claimed it wanted more information but there was truck loads of information.

"What the Government is doing by delaying is probably costing this country another 60 lives on the roads and costing literally hundreds of millions in avoidable costs and, of course, enormous human suffering."