Key Points:

National leader John Key yesterday revealed that he was interviewed by the Serious Fraud Office over the multimillion-dollar Equiticorp scandal - but felt his evidence would have helped to convict those involved.

In a bid to blunt Labour attacks on his credibility, Mr Key said he suspected his opponents would use either his role at Elders Merchant Finance or the fraud office interview in an attempt to slur his character.

He told the Herald he was questioned by the SFO about a lunch he had with a colleague soon after he left his job as foreign exchange dealer at Elders Merchant Finance, which was involved in Equiticorp's sale of NZ Steel in 1987.

But he said he had "nothing to hide" as he had left the company before the deal was conceived.

If anything his subsequent evidence would have helped result in prosecutions of those involved.

Senior Labour ministers have recently referred to the "H-Fee" in Parliament, and there are reports that Labour has been boasting of having a "neutron bomb" against Mr Key.

The "H-Fee" term appears to be a reference to sham foreign exchange deals set up by Elders IXL for a A$66.5 million payment to Equiticorp boss Allan Hawkins in 1987.

Hawkins and Elders director Ken Jarrett were jailed for their involvement in the deal.

The "H-Fee" is the subject of the latest in a series of attacks by Labour on Mr Key.

These include highlighting inconsistencies in his comments on Iraq, his use of different company and electoral addresses and, yesterday, his business links with architects facing leaky-building claims.

Mr Key said he left Elders Merchant Finance in 1987 three months before the "H-Fee" was dreamed up and knew nothing of it.

"So Labour is sitting there thinking, 'We've got this guy. John Key's done the foreign exchange deal'," he said.

"Just one small issue: Three months before any of those deals got decided, I had left Elders. I never did the deals, I never knew about the deals, and wasn't involved in them."

Mr Key said the SFO asked him years later about a lunch he had to celebrate his new job at Bankers Trust with his successor at Elders, Paul Richards.

He said Mr Richards had to leave the lunch at Plimmers restaurant to go to meet Elders director Ken Jarrett, who had travelled to New Zealand from Australia.

When Mr Richards returned he told Mr Key he had met Mr Jarrett, but did not discuss the meeting further, apart from saying it was bizarre.

Mr Key said Mr Jarrett later denied he was in New Zealand on that date and a few years later Mr Key was called in by the SFO to back up Mr Richards' claims that he had left the lunch to meet Mr Jarrett.

Mr Key said he might have been called as a witness, but in 1993 Mr Jarrett admitted his role in setting up the H-Fee and gave evidence against other Elders' executives.

In another development, Truth newspaper yesterday ran an article saying Mr Key was a director and shareholder in commercial property company Earl of Auckland Ltd.

Fellow directors include Colin Leuschke and Brian Cocker, who have put their architecture company - involved in at least three leaky-homes cases - into voluntary liquidation.

In Parliament, Cabinet minister Clayton Cosgrove said Mr Key needed to explain how the partnership fitted with his comment that greater commercial accountability was the way to ensure leaky-homes problems were not repeated.

Mr Key said that if he were involved in a company not acting fairly or morally, the questions would be justified, but he was not.

"I'm not in a business that is trying to avoid its liability in leaky homes."

One of Labour's main attack men, Pete Hodgson, yesterday said the matter was not an attack on Mr Key's integrity, but "I am raising concerns about the type of people he's happy to do business with".

Mr Key said he had known Mr Leuschke for many years and had never known him to act unethically. If it was ever proven that Mr Leuschke had acted unethically, "I will exit my business relationship with him".

Mr Leuschke has recently paid about $100,000 in a settlement with Auckland City Council over one leaky apartments block in Eden Terrace.