Increasingly less popular Prime Minister Malcolm Turnbull has denied he received any forewarning of a controversial Australian Federal Police raid on Labor offices in Melbourne related to NBN leaks.

Liberal senator Mitch Fifield, the current Communications Minister, issued a statement on Saturday revealing he knew federal police were investigating alleged NBN Co leaks, but said he did not tell the Prime Minister’s office.

“I was advised by NBN that the matter had been referred to the AFP,” Communications Minister Fifield said in the statement.

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“I did not instruct nor request them to do so.

“As an AFP investigation was underway, I did not advise other ministers or the prime minister of this matter.”

The timing of the late-night Thursday raid, in week two of a heated election campaign, angered Labor, obscured two days of Coalition talking points — and may affect Mr Turnbull’s already worsening polls.

According to a Fairfax-Ipsos poll published on Sunday, 48 per cent of voters approve of Mr Turnbull’s performance as prime minister and 38 per cent disapprove. This is a lower approval rating than Julia Gillard scored after her close 2010 campaign against Tony Abbott, Fairfax reported.

Labor leader Bill Shorten also narrowed the margin in the preferred prime minister stakes. In October, Mr Turnbull’s lead was 67-21. In the latest poll, this dropped to 47-30.

‘Turnbull must have known’

Shorten’s party took full advantage of the political opportunity the raid offered. On Saturday, the Labor leader described Senator Fifield’s statement as “explosive revelations” and said it was “inconceivable” and “totally implausible” that Mr Turnbull’s office wasn’t told.

“It is either gross incompetence or far worse and we are not being told the truth,” he told reporters in Sydney.

Labor politicians were careful not to insinuate that federal police acted improperly. But its senior politicians hammered the point that the government must reveal exactly what it knew in advance of the raid.

“Malcolm Turnbull needs to realise that Australians will not let him run and hide from the truth. Australians are distinctly and deeply unimpressed that this government and Malcolm Turnbull will go to such lengths to hide the truth from Australians,” Mr Shorten said.

“The public have a right to know, the media have a right to publish. Mr Turnbull needs to come clear and explain what he knows and what he has been told, or indeed what his staff and representatives have been told.”

Mr Turnbull tried to talk about other matters during his visit to the NSW marginal seat of Dobell, such as a promise to devote $30 million to support local parks, but journalists were preoccupied with the raid.

In response to questions, the Prime Minister confirmed his Communications Minister’s version of events, saying it was “entirely appropriate” he was not informed.

Other Liberals tried to qualify Senator Fifield’s statement, saying what he mean to say was that he knew generally about the NBN leak investigation, but not about the raid specifically.

A battle over privilege

Meanwhile, Labor senator Stephen Conroy has claimed parliamentary privilege over documents seized from his office during the Thursday night raid.

This means federal police cannot inspect the documents — which Senator Conroy said included Labor’s unreleased NBN policy — until the Senate decides if privilege does in fact apply.

Prime Minister Turnbull accused the Senator of using privilege to “keep the police away”.

“I don’t want to get into the legalities of Senator Conroy’s determination to keep the police away from these documents, which were clearly stolen from the NBN Co,” he told reporters on Saturday.

“He’s trying to keep the police away from those.”

Labor campaign spokesperson Senator Penny Wong accused Mr Turnbull of making light of the privilege claim.

“Parliamentary privilege isn’t the plaything of any government or any political party,” she told reporters in Melbourne.

“It is a principle that’s been around for many centuries.”