Trevor Mallard has scored an embarrassing own-goal by attacking an American billionaire who has not only donated money to Labour but has also supported the Government in its bid for a free-trade deal with the United States.

Prime Minister Helen Clark is understood to be furious over Mr Mallard's surprise attack on National's campaign finances.

On Thursday, Mr Mallard said there was no doubt that "the lead bagman" for National Party leader Don Brash was an American.

He confirmed later that billionaire Julian Robertson was at least one American Labour had in its sights.

But by last night the reportedly unscripted attack had backfired badly and Mr Mallard was not commenting to the media.

Te Tai Tokerau MP Dover Samuels reluctantly confirmed yesterday that Mr Robertson had made a donation to his 1999 election campaign, which Electoral Commission records show was $1000.

Compounding the frustration for Helen Clark is the important role Mr Robertson has taken in recent years supporting New Zealand's bid for a free trade agreement with the United States.

The Herald reported in April 2003 that he was influential in ensuring bridges were rebuilt quickly after the Prime Minister angered the Bush Administration with her comments on the Iraq invasion.

Helen Clark's spokesman said last night that a $1000 donation to a Labour MP six years ago would not stop the party raising issues about where National's campaign money was coming from.

The spokesman revealed that the Prime Minister had been aware for years of Mr Robertson's donation.

National Party general manager Steven Joyce called the revelation about Mr Samuels "amusing" but refused to comment further. A spokesman for Dr Brash said he would not comment either.

Earlier yesterday, Dr Brash indicated that National wanted to concentrate on releasing policies, such as one on tertiary education tomorrow and another on resource management on Monday.

"I invite New Zealanders to decide which party is focused on issues that will give their families a better future, and which parties are looking to conduct a shameful brawl in the gutter," he said.

Labour president Mike Williams said the revelation about the donation was neither embarrassing nor surprising given Mr Samuels was an important person in Northland.

Labour was yesterday changing its billboards and other advertising in a shift away from its achievements to targeting Dr Brash's past comments on issues such as Iraq, ending the country's nuclear-free status and free-market reforms.

Mr Robertson was a "very right-wing activist", said Mr Williams.

"If you Google him on the internet you discover he gives hundreds of thousands of dollars to the Republican Party."

The Weekend Herald did, and found him listed on the "National Taxpayers Union Foundation" website ranked sixth for donations to US parties between 1993 and 1997, having given US$484,000 ($704,000) to the Republicans.

Asked why a right-wing activist would help to fund a Labour MP's campaign, Mr Williams replied: "It's a local friendship, that's all."

Mr Samuels initially refused to comment yesterday but rang back to confirm the donation. He said he got to know Mr Robertson and his wife, Josie, over a number of years.