Tauranga MP Simon Bridges is among several Government politicians who are using a loophole to own properties which are not declared.
This has allowed the MPs to claim up to $77,000 in taxpayer-funded subsidies each year to pay off the mortgage.
An investigation of property records for all 121 members of Parliament has discovered that under an exception in the rules of the Register of Pecuniary Interests, six National MPs use their private superannuation schemes to own property that does not need to be disclosed - unlike assets held in trusts.
All six - Chester Borrows, Mr Bridges, Anne Tolley, Chris Auchinvole, Peseta Sam Lotu-Iiga and Mike Sabin - live in the Wellington properties while working in the capital and claim the accommodation allowance or expenses. Ministers get a flat annual fee of $37,500 ($720 a week) while backbench MPs can claim up to $24,000 in accommodation expenses.
By owning the property in a private superannuation scheme, the politicians can also use their taxpayer-funded superannuation subsidies to pay off the mortgage.
For every $1 placed in the private schemes by the MP, the taxpayer contributes $2.50 to a maximum of $28,920 - an annual superannuation total of up to $40,488.
Combined with the taxpayer-funded accommodation allowances, a minister like Mrs Tolley could pay off up to $77,988 of the mortgage each year while also making a capital gain as the property's value increases.
Mr Bridges, Mr Sabin and Mr Auchinvole all said they would have no problem with disclosing the properties, but had been advised by the Registrar for Pecuniary Interests not to do so.
Mr Bridges said he had listed both properties in Wellington and Parnell in his initial return, but was given advice to take them out. "If I'd forced the issue to put them down, I'm sure I could have, but if the rules don't provide for that or don't require that, my role in this is to comply with the rules and not more."
He had bought the Wellington apartment after becoming a minister because of the extra time he had to spend in Wellington. "It literally is my superannuation scheme ... It's my way of having something for the future."
Mr Sabin said he set his up because he did not have KiwiSaver, and a personal scheme gave him greater flexibility. He had bought an apartment rather than stay in hotels because he had to spend four nights a week in Wellington due to the travelling time from his Northland home.
He said the Registrar of Pecuniary Interests had instructed not to disclose properties in super schemes.
Mr Auchinvole said the intention was to give him a Wellington base, rather than to benefit from capital gains.
Mr Bridges also had a property in Karikari in his name, but explained he was a trustee for a friend and had no financial interest in it, so had not disclosed it.
When told a rule clarification in 2011 meant MPs had to list all trusts they acted as trustees for, whether or not they had a beneficial interest, he said he would put in a late disclosure of his role as a trustee.
Mr Lotu-Iiga said his apartment was a superannuation investment. He too said he did not have a problem with disclosing it, but was advised not to.
Mr Borrows said he was a beneficiary of the super trust he established, which owned his Wellington apartment.
Mrs Tolley would not say why she put her property into a super scheme, saying simply that she had abided by the legal requirements for the register.
Meanwhile, other MPs have disclosed assets.
Labour's Chris Hipkins has listed a rental property in Paraparaumu as owned by his super trust, and Labour's finance spokesman, David Parker, has listed share ownership and a property in Alexandra, which are held in his personal super trust.
The Green Party was criticised in 2009 - before the rules changed - after it was discovered its super fund owned two properties rented by Green MPs, who then claimed the accommodation allowance. The $48,000 claimed for both properties was then channelled back into the superannuation fund.
The party apologised and repaid $6000. Co-leader Metiria Turei later announced the sale of both properties. APN News and Media