Finance Minister Michael Cullen is accusing John Key of lying over his Tranz Rail shareholding after the National leader was forced to admit he had owned more shares than was previously thought.

Cullen last night released the results of Labour's research into Key's shareholding in the company before it was purchased by Toll Holdings in 2003.

In July this year, Key demanded Prime Minister Helen Clark apologise for suggesting he was engaging in insider trading in Tranz Rail shares after she claimed he had asked a series of questions about the company while a shareholder.

Key said his family trust had held Tranz Rail shares but sold them in June 2003, before he began commenting on the company as associate transport spokesman that same year. He did not correct media reports that his shareholding was limited to 30,000 shares held by his family trust.

Last night Key admitted on TVNZ that he had held 50,000 shares in the company, and that he had purchased at least some of the shares himself. Moments later he corrected himself, saying the amount was 100,000 shares.

"Actually maybe 100,000 from memory, sometimes 50,000, sometimes 100,000, yep," he said. "Yeah, sorry, there was 100,000 in total."

Asked why he had not corrected media reports at the time that his shareholding was limited to 30,000 shares, Key said: "No-one ever asked me the number I owned."

Key's defence is that used by Clark when questioned by Key about why she did not declare her knowledge of Owen Glenn's $100,000 donation in the Winston Peters affair. Both leaders have accused the other of being untrustworthy.

Key said last night he did not believe he had done anything wrong. He had sold all his shares on the date he had stated.

He denied acting on any inside information and said he still lost almost $100,000 on the deal.

However, Cullen said information on Key's share trades unearthed by Labour showed Key had bought more shares in the company, owning them while meeting Rail America to hear its views on the company.

He sold them a day before questioning Cullen at a select committee on Tranz Rail, but his family trust still owned its shares for a further two days.

Cullen said Key should have disclosed this shareholding to the committee. He also released copies of Official Information Act requests by Key to his office seeking more information on official discussions on the potential sale of Tranz Rail in April 2003, before selling his shares.

Cullen said Key had acted unethically and in breach of Parliament's rules because he did not declare his shareholding.

"John Key lied because he knew he had something to hide," Cullen said. "Mr Key has spent a lot of time over the last few weeks attacking the character and credibility of others.

"He has said people should not have to wait for direct questions to provide relevant information to the public."

- © Fairfax NZ News