Labour has accused John Key of lying over his ownership of Tranz Rail shares amid revelations the National Party leader failed to fully disclose his interests.
Mr Key's interests became an issue earlier this year when Labour claimed a conflict of interest because he had asked parliamentary questions about the Government's planned buyback of the country's rail tracks while he still had a shareholding in the rail operator.
Despite his role at the time as National's associate transport spokesman, he did not disclose his shareholding.
When Mr Key was questioned on the issue this year he said his family trust had held 30,000 shares in the company, but had sold them on June 9 and June 12, 2003.
He said his questions and comments never led to any gains from the company's share value.
But Finance Minister Michael Cullen today released correspondence and share register information contradicting several of Mr Key's claims.
The information showed Mr Key, through his trust and under his own name, had owned 100,000 rather than 30,000 Tranz Rail shares.
Questioned on the issue before he was aware the information had been released, Mr Key told One News his shareholding ranged between 25,000 and 50,000 shares up until June 2003.
But when pressed on the issue he admitted there were more shares.
"Actually maybe 100,000 from memory, sometimes 50,000, sometimes 100,000, yep," he said.
"Yeah, sorry, there was 100,000 in total."
Mr Key said no one had questioned him previously on exactly how many shares he had owned.
The papers released by Dr Cullen show Mr Key personally bought 50,000 shares in Tranz Rail in May 2003 after he had actively pursued information from the Government on the company.
He sold those shares five weeks later for $51,000 - more than double their $22,500 purchase price.
However, 50,000 shares bought by his family trust in February 2002, were sold in June 2003 at a loss of $132,000.
Dr Cullen said Mr Key should have declared his shareholding to Parliament and his failure to do so was unethical.
"John Key lied because he knew he had something to hide," he said.
"Mr Key was in fact commenting publicly on Tranz Rail, meeting with bidders for the rail track and vigorously pursuing the release of commercially relevant information all while being an undisclosed shareholder in the firm."
Dr Cullen said Mr Key had spent a lot of time attacking Prime Minister Helen Clark's credibility over the New Zealand First donations scandal, but had covered up his own actions.
"For him to have in effect grossly misled both the media and the public on this I think raises that issue of trust yet again," he told reporters.
"Clearly Mr Key was not simply not forthcoming, he actually lied."
Timeline of National leader John Key's Tranz Rail share dealings.
* February 15, 2002 - Mr Key's family trust buys 30,000 shares in Tranz Rail for $108,000;
* February 19, 2002 - the trust purchases 20,000 more Tranz Rail shares for $72,000;
* July 27, 2002 - Mr Key is elected to Parliament;
* October 30, 31, 2002 - Mr Key asks parliamentary questions relating to Tranz Rail and the future of the rail track without disclosing his shareholding;
April 9, 2003 - in Parliament, Mr Key questions Finance Minister Michael Cullen about secret meetings between the Government and Tranz Rail;
* April 14, 2003 - Mr Key seeks dates and details of government meetings with Tranz Rail in written parliamentary questions;
* April 23, 2003 - Mr Key seeks copies of minutes from Government meetings with Tranz Rail from Dr Cullen, but is declined on commercial secrecy grounds;
* May 7, 2003 - Mr Key purchases 50,000 more Tranz Rail shares in his own name for $22,500;
* May 20, 2003 - in his role as National's associate transport spokesman Mr Key meets Rail America to discuss its views on Tranz Rail;
* June 10, 2003 - Mr Key sells the 50,000 Tranz Rail shares he purchased in May for $51,000;
* June 11, 2003 - under questioning by Mr Key in Parliament, Dr Cullen expresses his view that Tranz Rail is carrying hundreds of millions worth of liabilities;
* June 13, 2003 - Mr Key's family trust sells its 50,000 Tranz Rail shares for $48,000 - a loss of $132,000.
* June 18, 2003 - Mr Key again attacks the Government's plans to buy back the rail tracks.
* October 16, 2003 - Mr Key makes an apparent hypothetical reference in the debate over Pecuniary Interests Legislation to a possible shareholding in Tranz Rail.