Key Points:

The former boss of the Serious Fraud Office has supported John Key's claims that he was clear of any involvement in the 1980s Equiticorp H-Fee scandal, saying to hint otherwise was purely "mischief making".

Charles Sturt, the former SFO director who investigated the Equiticorp deals and took them to prosecution for fraud, yesterday confirmed Key's account of his interview with the Serious Fraud Office.

Mr Key was questioned during fraud investigations into the H-Fee - two sham foreign exchange deals by Elders IXL in 1988 to pay A$66.5 million ($76.6 million) after the purchase of NZ Steel from Equiticorp. Mr Key had left his job with Elders some months before the deal and says he had no knowledge of it.

Mr Sturt said Mr Key was simply one in a "vast array of innocent people, potential witnesses, in a massive fact-gathering exercise. I feel compelled to fully support the reported comments of John Key in relation to the H-Fee transaction. It should not need to be said that John Key was completely innocent of any wrongdoing whatsoever. For any politician to hint or suggest otherwise would be absolutely rubbish and pure mischief-making".

Mr Key told the Herald of his interview with the Serious Fraud Office, saying he wanted to pre-empt any attack about any alleged involvement in the Equiticorp scandal after Labour Minister Trevor Mallard referred to the "H-Fee" in Parliament.

Mr Key believed Mallard was referring to his time as a foreign exchange dealer at Elders Merchant Finance in the 1980s. He says the evidence he gave - in which he confirmed his successor at Elders had to leave a lunch with Key to meet with Elders executive Ken Jarrett - could only have assisted in building a case against the fraudsters.

Yesterday Labour Ministers were denying any knowledge of the H-Fee rumours and Labour Party president Mike Williams said the news was "a bolt from the blue" for him.

Mr Mallard admitted using the term in interjections in the House but refused to comment any further.

Health Minister Pete Hodgson said he did not know of the H-Fee rumours and said Mr Key had "clearly got spooked. I'm obliged to take him at his word but you can't help feeling there's more coming".

He said he did not know of any specific forthcoming information.

"That's not an accusation or threat, but it's just that part of New Zealand history when there was an awful lot of laxity around what would be considered inappropriate business."

National deputy leader Bill English said attacks on Mr Key's credibility were a sign of panic by Labour.

However, Labour is unlikely to pull back in its spate of attacks on Mr Key, which have so far included his comments on Iraq, his use of different addresses for official purposes, and his business ties with architects who designed buildings caught up in the leaky homes issue.