Police made error with Nicky Hager warrant, lawyer tells court

 Police failed to tell the judge who granted the warrant to search investigative journalist Nicky Hager's Wellington home the extent of their investigations into who hacked a blogger's emails, a court has heard.

Nicky Hager Source: Breakfast

Nicky Hager’s latest book ‘Dirty politics’ has prompted a series of official complaints. Source: 1 NEWS

Lawyers for Hager are in the High Court at Wellington arguing that the "extremely invasive" 10-hour raid in October 2014 should never have happened and was in fact unlawful.

Hager has sought a judicial review of the way police applied for a search warrant, the subsequent granting of the application, and how the search was carried out.

The raid took place in the aftermath of the release of Hager's book, Dirty Politics, which was based on information taken from Whale Oil blogger Cameron Slater's emails and online communications.

The information was given to Hager by an anonymous hacker and the search was carried out as part of the police investigation into who was behind the alleged hacking of Slater's computer.

Hager's lawyer Felix Geiringer told the court on Tuesday that when police applied for the warrant, they failed to tell the full story about the state of their investigations at that point.

When they applied for the warrant to search Hager's house, police hadn't yet sought a United States court order to allow them access to information held by Google and Twitter.

"None of this was told to the judge," he said.

Police also should have said they were following up another line of inquiry after material taken from Slater's online accounts was posted online and linked to on Twitter.

"What had to be there was a full explanation of all the incomplete inquiries," Mr Geiringer said.

On Monday, the court was told that as a journalist, Hager has a presumptive right under the law to keep his sources secret.

That protection given to journalists and their sources is a fundamental part of the democratic process.

If police are able to carry out raids or searches on journalists and force them to reveal information, "that would have a chilling effect on future informants", Hager's lawyer Julian Miles QC said.

The hearing before Justice Denis Clifford is expected to wrap up on Wednesday.