"So in fact, if you're looking for secrecy New Zealand is the wrong place to come because we are not going to provide that secrecy."
However, despite his initial insistence that the trust regime was a tight shop, he has now signalled the Government would make changes to the disclosure rules if a review by tax expert John Shewan recommended it.
The Government could also bring forward a second tranche of anti-money laundering measures. Mr Key said while it was possible there were rogue trust companies, they had to meet laws, include money laundering laws, and Inland Revenue was recently given $205 million for compliance.
Existing rules already required foreign trusts to be registered and to keep detailed records which could be requested by Inland Revenue and passed on to tax authorities in other countries.
However, United Future leader Peter Dunne, who was Revenue Minister from 2005 to 2013, stopped short of describing New Zealand as a tax haven, but said the papers raised a risk it would be perceived as a tax haven and that was just as dangerous for its international reputation.
Mr Dunne said he was concerned Inland Revenue had not alerted him to the "explosion" in the number of foreign trusts setting up in New Zealand when he was the minister.
Mr Key said a "crack squad" from Inland Revenue were preparing to trawl through the full set of data which will be released at 6am on Tuesday morning. The 11.5 million files were leaked to German newspaper Suddeutsche Zeitung which provided them to the International Consortium of Investigative Journalists.