Helen Clark is facing intense political pressure to dispel claims that she was involved in the downfall of top policeman Peter Doone.

He intends to sue her for defamation.

Mr Doone, the former Police Commissioner, was forced to resign from his $275,000-a-year job after a late-night incident in which he and partner Robyn Johnstone's vehicle was stopped by two police officers on election night in 1999.

Court papers released yesterday revealed that the Prime Minister told the Sunday Star-Times she believed Mr Doone had made a remark which might have meant a rookie constable did not breath-test Ms Johnstone, now Mrs Doone.

The four words "That won't be necessary", which Helen Clark confirmed she understood Mr Doone said to Constable Brett Main, who was holding a breath-test sniffer device, are pivotal.

Mr Doone has always denied he said that and the newspaper later apologised, saying it accepted the comment was not made.

But the scandal effectively forced him from his job in January 2000, although he worked as a constable in the Department of Prime Minister and Cabinet for six months to serve out his notice.

He has argued that he lost pay and superannuation as a result.

Helen Clark is in Turkey but she said through a spokesman that the Sunday Star-Times had confirmed she was not the original source of the remark. That source is believed to be a police officer. The Prime Minister also said she would vigorously defend any legal action.

Mr and Mrs Doone sued the Sunday Star-Times' publisher Fairfax New Zealand for defamation, but yesterday dropped the action saying they would now be suing a prominent New Zealander.

Other court documents revealed that person to be Helen Clark, and that she had provided a brief of evidence for Fairfax in which she confirmed telling the newspaper's editor and reporter she understood the four words had been uttered.

The Herald understands Helen Clark did not volunteer a statement, but was subpoenaed to do so by the newspaper's lawyers.

This unusual move was contrary to the established newspaper practice of refusing to provide information that could identify a source.

It is also understood the newspaper would not have published without the Prime Minister's confirmation. It believed the four words were to be included in an official Police Complaints Authority report on the incident, but they were not.

A key issue for the Prime Minister will be whether she believed what she said to be true.

Last night, Opposition parties National and Act were urging her to tell the public if she had deliberately intended to put pressure on Mr Doone to go.

National Party leader Don Brash said it would be "an absolute outrage" if Helen Clark had leaked or confirmed information to the media in order to undermine Mr Doone.

Act leader Rodney Hide asked if Helen Clark had "knifed ... Mr Doone in the back" by leaking or confirming false information.

He said it was shocking that the information she gave to the media might have been wrong.

The Prime Minister's confirmation of the remark to the newspaper came four days after then Attorney-General Margaret Wilson wrote to Mr Doone's lawyer expressing concerns about whether the commissioner could stay in his job because of the incident.

Mr Doone was invited to reply by January 25, but two articles appeared in the meantime.

The Doones have not filed any proceedings against Helen Clark yet, but Mrs Doone said it would be done as soon as the legal work was completed.

'Why have we been stopped?'

Just after 9pm on November 27, 1999, a police constable stopped a car on a wet Wellington night.

Brett Main, who had been on the job just three days, got out to talk to the woman driver of the 1999 Nissan Maxima that had been travelling without lights. But he never interviewed or breath-tested driver Robyn Johnstone, who had drunk "two or three" glasses of wine, after her partner, then Police Commissioner Peter Doone, got out of the car and intervened.

According to an investigation at the time, undertaken by then Deputy Commissioner Rob Robinson - now the country's top policeman - Mr Doone asked Constable Main: "Why have we been stopped?"

Constable Main, who did not immediately recognise Mr Doone, replied: "Because you didn't have your lights on and I would like to speak to the driver."

When he realised he was speaking to the commissioner, the constable said he "felt nervous and overawed".

Mr Robinson found insufficient evidence to warrant a case of obstructing police against Mr Doone, and then-Solicitor-General John McGrath agreed.

Mr Robinson, whose report was forwarded to the Police Complaints Authority, called Mr Doone's actions "inappropriate". The authority concluded Mr Doone's actions were "undesirable". Mr Doone resigned in January 2000.

Couple's PM 'shock'

New Zealand's former top policeman, Peter Doone, last night spoke of his shock when he found out Prime Minister Helen Clark was involved in the newspaper story he blames for his downfall.

Mr Doone and his wife, Robyn, said they learned last week, from court documents, of Helen Clark's involvement.

"It's hugely shattering from a personal perspective for both of us," Mrs Doone said.

But the couple seemed relaxed last night as they posed for photographs - given that they are preparing to sue the Prime Minister.

"I don't want to look too happy, and I don't want to look too serious," Mr Doone said, as the photographer snapped away.

"I want you to have a serious face, because this is a serious issue," said Mrs Doone, a former communications manager.

Mr Doone said his lawyer, John Upton, QC, was drafting papers and they would be taking legal action as soon as possible.