Just days before the Transport Minister announced a major bridge upgrade for Northland, he was told one of the bridges he selected could not be widened because of nearby kauri trees.
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The advice from the Transport Agency which has been released to Radio New Zealand under the Official Information Act was subsequently ignored by the Minister Simon Bridges.
During the Northland by-election campaign Mr Bridges announced the Government would double-lane ten bridges which are currently single-lane.
Three days before he made that announcement, the Transport Agency advised his office that the Darby and Joan Bridge in the Waipoua Kauri Forest "could not and should not" be widened.
The bridge was built when the road through the forest was sealed in the 1990s and won an environmental award for its design, which deliberately protects the roots of the kauri on either side.
The local iwi Te Roroa has said there is no way it would let the government chop down kauri to expand the bridge.
New Zealand First leader Winston Peters accused Mr Bridges of incompetence.
He said he was not surprised Mr Bridges ignored the official advice.
"They thought they could come up and make a whole lot of blithe promises to the people of Northland and win an election and they found out they couldn't. But the question is, are those ministers going to be held to account?"
Mr Bridges is refusing to say why he ignored the Transport Agency's advice but said the Government intended to ensure the two kauri remain.
Labour says Minister should be sacked
Labour leader Andrew Little said Mr Bridges should be sacked because he has breached the cabinet manual.
Mr Little said Mr Bridges asked for advice from the Transport Agency about project to upgrade the bridges and the cabinet manual said Ministers should not go to Government departments asking for advice on matters relating to an election.
He said if he was Prime Minister he would remove Mr Bridges' ministerial warrants.
"A cabinet minister, Simon Bridges, sought advice from a Government department at the time of an election in relation to a pledge that they were making in that election.
"He's breached the cabinet manual [and] the Prime Minister, if he has any standards at all, has to take action against Simon Bridges."
Prime Minister John Key said ministers were allowed to use the resources of officials [during an election campaign] in terms of what would be Government policy.