Former National Party minister Anne Tolley says she shared confidential details of Winston Peters' pension overpayments with family members and staff.

She also says one of her senior advisors passed the information to other staff members in her office - despite her strictly advising him not to.

Giving evidence in the High Court in Auckland today, the former Social Development Minister said she was not responsible for the information making its way into the media a month before the 2017 general election.

Tolley also had no reason to believe her staff had leaked the information.

She first learned of the issue at a weekly meeting with former Ministry of Social Development chief executive Brendan Boyle on July 31, 2017. They were the only two people in the room when he told her Peters had been overpaid in his pension since 2010, that MSD had been alerted when his partner applied for superannuation in 2017, and that he had paid it back.

After the 10-minute briefing, she said she felt the matter had been resolved.

Peters has argued that she should have asked whether it was necessary to get the briefing, but Tolley said this was a decision for Boyle to make.

After the meeting, Tolley briefed her senior adviser, whose name is suppressed, and said the information was strictly confidential and not to be shared. She said she briefed him in order to get advice about whether she should ask for the briefing to be put in writing.

Tolley said she was "surprised" to later learn that her adviser had shared the information with other staff in her office. She said this was "contrary" to her strong urging that it be kept secret.

She also later discovered that a staff member who had been seconded to her office from MSD knew about Peters' overpayments.

"That was expressly against my instructions," she said.

After speaking to National Party chief of staff Wayne Eagleson, Tolley decided to ask for a written briefing about Peters' case, which was placed in a safe in her office by a private secretary and later shredded when the government changed.

When Tolley returned home to Ohope at the end of the week, she said she told her husband about Peters' overpayments and said he had to keep it in absolute confidence. They were the only two people in the house at the time.

Tolley said there was one more occasion where she mentioned the Peters issue to another person.

While Tolley was at a National Party conference in Queenstown in late August, she had lunch with her sister at a cafe.

Her sister praised Peters, and Tolley responded by saying that the New Zealand First leader was "not as great as she thought he was". She then told her sister that he had been wrongly overpaid his pension for seven years. She made the comment in passing and did not provide much detail, she said.

"I sincerely regret my outburst with my sister. I was tired and I was cross," she said during cross-examination by Peters' lawyer Brian Henry.

The details about Peters' superannuation case appeared in media the same weekend of that National Party conference. Tolley said the details were published before she spoke to her sister about it.

Tolley said she did not make the anonymous calls to two newsrooms, which alerted media to Peters' overpayments. She did not arrange for the calls to be made, she said.

Henry went on: "Do you agree with the general proposition that when you disperse highly incendiary information like this, it goes to someone who may be trustworthy. They get tired, a bit cranky, a little bit intoxicated, and it comes out."

Tolley said she was not drunk when she made the outburst to her sister.

"I wasn't saying you were," Henry said.

"I wasn't," Tolley said.

She added that she would not share information with someone who would disclose confidential information in this way.

Henry pointed out that she did that herself when she told her sister.

"I did, and I regret it," she said.

Tolley said she could rule out her husband, sister and Eagleson leaking the information. She was disappointed in her senior advisor but said he did not know the information which was eventually published in the media - such as the amount Peters had been overpaid ($18,000).

She said she also had a brief conversation about the case with then-State Services Minister Paula Bennett, who was later briefed about it by her officials. Bennett will give evidence later today.

Peters says his privacy was breached when his pension information made its way into media in August 2017. He has not pointed the blame at one person or organisation, but is jointly accusing the two ministers, public sector bosses and MSD of breaching his privacy.

Peters was overpaid after filling out his application form incorrectly in 2010, which led to him receiving the more generous single person's pension. The error was not picked up until his partner Jan Trotman applied for superannuation in 2017.

Under cross-examination, Peters' lawyer Brian Henry asked Tolley whether she had breached Boyle's confidence by speaking to her senior advisor about Peters' overpayments.

The office handled sensitive information about private individuals and she had no reason not to trust her staff, she said.

When Henry said this was different because the information about a political rival a month out from an election was "dynamite", Tolley said she had no reason to suspect her staff leaked it.

BENNETT IN THE WITNESS STAND

National Party deputy leader Paula Bennett also gave evidence today.

She told the court that when speculation arose in August 2017 that a political scandal was about to be published, there were initially concerns within her party that it could relate to false allegations which were circulating around her.

These false allegations were about her personal life before becoming an MP, Bennett said. They were being aired on social media at the time.

Newsroom co-editor Tim Murphy had tweeted that the "mother of all scandals" was about to break.

Bennett spoke on the phone to then-Prime Minister Bill English, who was aware of the speculation about her and knew that it was untrue, she said. He was concerned about her wellbeing.

Bennett told English that she thought the imminent stories would be about Peters and not her. Asked why she thought this, she told English that Peters' pension had been overpaid - as she had learned in a "no surprises" briefing by officials in her State Services portfolio earlier that month.

This conversation between Bennett and English occurred after Murphy's tweet, and after newsrooms had received anonymous calls telling them about the case, Bennett said.

Bennett was briefed about Peters' case by State Services Commissioner Peter Hughes and his deputy Debbie Power on August 1, 2017. They were the only three people in the room for the meeting, which lasted 10 minutes.

Under cross-examination, Bennett expressed her frustration that she had been wrongly linked to the leak.

There had been "many allegations" and they had as much validity as the previous rumours about her personal life, she said, her voice rising.

Bennett said she did not think the pension overpayments were a scandal, especially given Peters had said he would pay back the money.

She said she thought "good on him" and that the public would think similarly.

Asked whether someone with the information might have leaked it while stressed or drunk, Bennett said: "I'm a Westie - if we've got something to say we say it straight to them not behind their back."