Analysis - The credibility of the Housing Minister is on the line after a week of shifting stories about a key element of KiwiBuild.

Photo: RNZ / Rebekah Parsons-King

The flagship house building programme is already under intense scrutiny after a number of controversies - the messy departure of former head of the KiwiBuild Unit Stephen Barclay, and the need for ministerial "recalibration" after serious teething problems.

Now Mr Twyford is under fire for a series of statements he and his ministry have made about the oversight of the Crown underwrite - hundreds of millions of taxpayer dollars committed to shift the risk from property developers to the Crown by promising a guaranteed price.

National Party housing spokesperson Judith Collins is calling for Mr Twyford to be sacked unless he can provide a credible explanation for why he told Parliament there was "extensive documentation" about the approval process, but was contradicted by the ministry shortly after which said there was no publicly available paperwork.

It all started with an official information act request from National to the ministry about the criteria developers had to meet to get the underwrite. Simply put, they had to show the financial backing of how the government would get developments moving more quickly and increase the supply of affordable housing.

Ms Collins cited the ministry's response in Parliament on Wednesday - that the required test was "done verbally with builders and no written record existed", prompting her to question if officials were playing "fast and loose" and it was all done with a handshake.

Surprised by that, Mr Twyford tried to clarify the situation and said the request had been misinterpreted by the ministry. He gave assurances the process was robust and there were "a number of communications and documents" officials would provide to back that up.

"While there is no specific single assessment document as requested by the National Party research unit, there are other documents and communications that set out the negotiations and record the ministry's work in this area", he told Parliament.

In the next hour he was repeating those assurances to reporters.

"I'm satisfied that they [ministry officials] are subjecting these contract negotiations to the kind of scrutiny they need and there is a trail of documentation to support that," he said.

But that was not the case.

Housing Ministry chief executive Andrew Crisp declined to speak to media, but issued a written statement saying "no such documentation exists as there is not a standalone additionality test".

The story then shifted to a statement there was written evidence developers had to prove their case for a Crown underwrite, but that was buried in commercially sensitive contracts the ministry is refusing to make public - even in redacted form.

'Additionality' is the officials' way of describing the criteria for the underwrite. The ministry said "additionality is assessed as core part of the business case for a KiwiBuild underwrite", rather than by a standalone test.

Again, this is contrary to past statements by the minister, who speaking in Parliament in March referred repeatedly to the additionality "test".

As recently as Wednesday, Mr Twyford talked about the ministry advising him "they apply an additionality test".

Minister being 'misleading' - Judith Collins

Ms Collins said the minister has to explain the discrepancies.

"What I've got is a situation of quite clearly misleading on this issue and the ministry saying there is no standalone additionality test - completely contradictory to what the minister said in the past."

She said the ministry response concerns her greatly because it "sounds as though it's just really how the developer and KiwiBuild 'feel' about the proposed deal, rather than a specific test".

Ms Collins said she did not buy the argument that details about the underwrite could not be released because of commercial sensitivity.

"The commercial details could in fact be redacted, which is quite standard when there is issue of particular commercial sensitivity."

It was potentially a serious breach, Ms Collins said, as the information had been requested through the Parliamentary process.

"We have asked those same questions in writing, and we now have entirely different answers between the minister and the ministry, and those answers are mutually exclusive.

"Someone needs to come up with a pretty good explanation, pretty quickly, or I'll be calling for Phil Twyford to be stood down", she said.

RNZ requested an interview with Mr Twyford, which he declined.

Through a spokesperson he reiterated there were documents, but the ministry was not releasing them because they were commercially sensitive.

He also said the additionality test was the ministry's term for its business cases.