National Party deputy leader Paula Bennett says Winston Peters should repay taxpayers the cost of his failed court action - estimated to be more than $1 million.
Meanwhile, the Serious Fraud Office (SFO) has confirmed it is on track to finish its investigation into the New Zealand First Foundation before the September election.
The New Zealand First leader and Deputy Prime Minister had taken court action seeking damages and a declaration that his privacy had been breached in the lead-up to the 2017 general election.
He claimed that details of his superannuation payments were leaked to media to publicly embarrass him and cause him harm.
A high court judgment released yesterday agreed with Peters, but the case against former Government ministers Paula Bennett, Anne Tolley and others fell over because Peters could not establish who was responsible for the leak.
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Bennett told the Herald this morning that it was wrong for the information to be leaked to the media, but she had no idea who was behind it.
"But you can't go casting shadows over other people and cost the taxpayer literally hundreds of thousands of dollars."
The Crown costs for fighting the case, not only for Bennett and Tolley but also public service bosses Brendan Boyle and Peter Hughes, are estimated to total more than $1 million.
Costs in the case were reserved and Bennett said it was up to the Crown to decide whether it wanted to recover any legal costs.
But she personally thought Peters should cover the lot.
"All of them," she said when asked if she meant her legal costs or those of all the defendants in the case.
"He talks about the damage to his own reputation, but he's been able to put aspersions on ours."
Peters' office has been asked whether he will cover the Crown's legal costs.
He said in a statement last night it was always going to be difficult to prove where the leak came from.
But he was pleased the decision recognised "a deliberate and malicious breach of privacy done with the intent to damage my reputation and cause harm".
In May 2017, the Ministry of Social Development discovered that Peters had been wrongly paid the single person's pension for seven years despite being in a long-term relationship with partner Jan Trotman.
Once alerted, he paid back the $18,000 difference and MSD decided not to open a fraud case.
Boyle alerted the State Services Commission, and Tolley and Bennett were briefed in their social development and state services portfolios under the "no surprises" convention.
The details of the overpayment made their way into media in August 2017, a month before the general election in which Peters was likely to play a key role.
Peters took legal action before he started negotiating with the National Party about a potential coalition after the 2017 election.
National has ruled out working with Peters after the election this year.
Meanwhile, the NZ First Foundation is under investigation by the SFO after the Electoral Commission found that money passed to the foundation should have been treated and disclosed as donations to the NZ First party.
This morning the SFO said the investigation was on track to be completed before the September 19 election date.
"We are progressing the investigation under the current lockdown restrictions and are still on track to complete it within that timeframe," a spokesperson says.
"However, our actual completion date will be dependent upon our ability to conduct certain interviews as well as other tasks which can only be completed at lower alert levels, and the cooperation of those who hold information relevant to our investigation."