Prime Minister Malcolm Turnbull has defended NBN chairman Dr Ziggy Switkowski after it emerged the telco executive breached election protocol and ignored political advice when opining on NBN’s right to pursue the source of damaging internal leaks.

A widely-published letter from the Department of Prime Minister and Cabinet secretary Martin Parkinson to Labor’s finance spokesman Tony Burke confirmed that parts of Switkowski’s May 28 opinion piece breached caretaker conventions.

Caretaker conventions, among other things, are designed to “protect the apolitical nature of the public service and avoid the use of Commonwealth resources in a manner to advantage a particular party” during an election campaign.

The practices are generally accepted but not legally enforceable.

Switkowski had opined to Fairfax Media on NBN’s right to call in the federal police to investigate the source of a series of data leaks that embarrassed the company and the Government over several months.

The leaks included data about delays to the fibre-to-the-node rollout and cost blowouts on remediating copper cable.

Labor offices were sensationally raided by police as part of the investigation, and two NBN employees were stood down.

“When dozens of confidential company documents are stolen, this is theft,” Switkowski opined after the raids took place.

“If an employee has strong personal conviction unsupportive of a company's strategy, they can argue their case with management or resign.

“They cannot give voice to their preferred ideology by passing on stolen documents.”

Labor immediately took issue with Switkowski’s incursion during an election campaign, referring the matter to the Department of Prime Minister and Cabinet (DPMC).

The response to that referral was damaging: it confirmed that parts of the opinion “are not consistent with established practices around caretaker conventions”, and that Switkowski ignored advice from DPMC not to publish.

That has placed renewed pressure on both NBN and the Government.

Prime Minister Turnbull said yesterday that he personally had no prior knowledge of the content of Switkowski’s piece.

He also defended Switkowski’s record at NBN and his right to publish.

“The caretaker convention, compliance with it, if you like, is a matter to be determined by the head of the relevant agency, in this case that is NBN Co and that is Ziggy Switkowski,” Turnbull said.

“He has explained why he made the statement that he did, why he felt it was operationally necessary and I respect his decision to do so.

“You can see the company was being accused in the public domain of very serious misconduct which was undermining the morale of 5000 people working for it and he felt that he had to set the facts straight and he has done that.

“But you have to remember, he is a very experienced man. He has been the chief executive of a big government business enterprise before, Telstra, when it belonged to the Government.

“He is one of our most distinguished corporate leaders and a very thoughtful one too.”

However, that defence is unlikely to satisfy critics.

Internet Australia blasted the substance of Switkowski’s opinion piece in the days following and has called for a “post-election review of the NBN”.

“Whoever wins the upcoming election should hold an independent review of both the strategic technical direction that NBN is now pursuing and the relevance and veracity of the reports it is making public,” Internet Australia CEO Laurie Patton said.