Australian Federal Police (AFP) commissioner Andrew Colvin has defended police raids at the Melbourne office of Labor’s deputy Senate leader Stephen Conroy and the home of an ALP staffer, saying the timing was driven by operational considerations.

Colvin said the government was only informed when the action had started late Thursday. He also rang Opposition Leader Bill Shorten.

Addressing a news conference in Canberra, Colvin said NBN Co referred leaks to the police in December. He said the leaking had been continuing while the police probe had been proceeding, indicating this had been behind the timing. “We believe that the offending has been ongoing throughout the conduct of that investigation. And that plays into our minds in terms of the operational strategies.”

Labor has claimed parliamentary privilege for the seized documents which Conroy, a former communications minister, had as part of a Senate inquiry. The opposition has pursued the performance of NBN Co when Malcolm Turnbull was communications minister.

Colvin said the documents had now been sealed and the police no longer had access to them. They would be lodged with the Senate.

The opposition said the raids were “extraordinary” and unprecedented. Shadow Attorney-General Mark Dreyfus questioned both the timing of the police action and the origin of the original referral of the leaking to the police. After Colvin’s news conference Dreyfus said he accepted what the commissioner had said about timing.

“It’s not about the Australian Federal Police,” Dreyfus said. “This is about why NBN Co has chosen to commence this investigation, why the government – because NBN Co answers to the government – has had this investigation undertaken and not much more serious potentially national security leaks.”

Labor’s question was “what were the conversations between the prime minister, between ministers, between staff of the prime minister and ministers and NBN Co that prompted this investigation and, on an ongoing basis, what did they know about this investigation?”, Dreyfus said.

Turnbull, who did not address those issues, sought to turn the attack back on Labor, declaring it was attacking the AFP’s integrity. “That is a shameful thing to do. Labor should be ashamed of themselves.”

He also broadened the issue to question Labor’s credentials on national security. “You can’t trust Labor on national security. We know where they stand or don’t stand on border security. Now we see them attacking the integrity of the Australian Federal Police.

"The only thing we should do with respect to this investigation is to let the federal police do their work.” He said he respected the AFP and “I believe all Australians respect them and so should the Labor Party”.

The warrants named two Labor staffers – Ryan Hamilton, who works for Shadow Communications Minister Jason Clare, and Andrew Byrne, from the Conroy office – and several media outlets: the ABC, The Australian, the Australian Financial Review, The Sydney Morning Herald, and Delimiter.

Colvin said an NBN staff member was present during the raid to identify documents. This was normal procedure, he said.

Labor’s Senate leader Penny Wong said the question of parliamentary privilege was critical to this matter because it went to the right of parliamentarians to do their job. Colvin said it was “not necessarily the case that parliamentary privilege will be afforded to those documents”.

Clare said Turnbull had “butchered the NBN”.

Update:

Bill Shorten told a news conference: “Mr Turnbull is going to extraordinary long lengths to stop Australians from finding out the truth about the cost blowouts in NBN.

"He is going after whistleblowers and he’s smearing his political opponents. The public has the right to know the truth and whistleblowers deserve protection.”

Shorten said NBN Co was “a creature of government”, and it was “inconceivable” that it would launch a police investigation and not make it clear to the owner of the company what was happening.

The revelation that Turnbull had managed to expand the cost of NBN from the A$29 billion he promised in 2013 to $56 billion was “massively damaging”, Shorten said.