Labour MP Pete Hodgson says legal advice to the Prime Minister over the status of his blind trust does not answer the question at the centre of his privileges complaint to Parliament's Speaker.
John Key set up the Aldgate Trust when he became Prime Minister to hold a number of investments and assets - a move aimed at ensuring there is no potential for conflict-of-interest issues.
But Companies Office records show that a company called Whitechapel, set up soon after the 2008 election, now owns assets previously held by Mr Key and his wife, including interests in an Otago vineyard, a dairy investment fund and an Auckland property firm.
On Friday, Mr Key released advice from the law firm that established his blind trust, which states that he has no influence or control over it or Whitechapel, the company that administers it. Mr Key has denied any knowledge of Whitechapel's existence.
Why was Whitechapel established? asks MP
Mr Hodgson's complaint alleges that Mr Key breached parliamentary privilege when he said his trust was so blind he could not know what assets he held.
The Labour MP says the legal advice released by Mr Key does not answer his question at the centre of his complaint.
Mr Hodgson says the Prime Minister can find out about the activities of the Aldgate Trust through Whitechapel - information about which is publicly available.
"Mr Key is holding the view that he never knew about Whitechapel - and I certainly can't show that he did," Mr Hodgson says.
"But it does beg the question as to why Whitechapel was established in the first instance. And that hasn't been established."
Mr Hodgson says it is unusual to establish a blind trust and then put a transparent company alongside it.
Mr Key's lawyer, Pravir Tesiram, says that although Mr Hodgson has claimed some of the Prime Minister's assets were transferred to Whitechapel, they were in fact sold.
The Speaker is yet to rule on Mr Hodgson's complaint.