Westpac handed over private details without judicial authorisation, though other firms declined, court documents show.

Detectives investigating the Dirty Politics hacker Rawshark sought the banking, telephone and travel records of author and journalist Nicky Hager without any search order or other legal power.

Court records show Westpac - the government's banker for 26 years - handed over "almost 10 months of transactions from Mr Hager's three accounts" at the request of detectives investigating the hacking of Whale Oil blogger Cameron Slater's email and social media accounts.

Other companies that were asked for Hager's private details told police to come back with a court order, which would have legally obliged them to surrender the information.

The details are revealed in documents obtained from the High Court by the Scoop news site, which intends to publish the full material today.

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The documents come from Hager's legal challenge to a police search warrant, which was executed on his Wellington home in early October last year. The High Court has yet to return a judgment on the case.

Hager's legal teams used police documents to detail how detectives sought information on him in late September last year - just after the election - from 16 "bank contacts", Air NZ, Jetstar, Spark, Trade Me and Vodafone. The request to Air NZ also sought information about anyone Hager might have been travelling with, the documents show.

Detectives told the companies they needed the information for an inquiry into "suspected criminal offending, namely fraud, dishonest access of a computer system", telling the bank the information would help avoid "prejudice to the maintenance of the law through the detection of serious offending".

The Privacy Act allows those holding personal information to waive the law if there are "reasonable grounds" to believe it would assist "maintenance of the law". There is no sign in the High Court documents of Westpac - or any of the agencies - being supplied with additional information that might assist with the "reasonable grounds" test.

The documents do show the other companies rejected the request without a legal order. Hager's lawyers said: "Police did not seek production orders for any of this information."

Westpac sent detectives transaction details from December 2013 until September last year, with other personal details.

The police decision to seek detailed information without a legal order appears contrary to the position stated by Assistant Commissioner Malcolm Burgess to the Weekend Herald last March.

He said there were "controls around how information is both requested and provided ... While the Privacy Act provisions can be used to access low-level information, such as basic account details, higher-level data must be obtained through a production order," he said.

The court documents show Detective Inspector Dave Lynch testified that the banking inquiry was intended to track Hager's travel movements and to see if there was a financial link to Rawshark. It was also to see if "he was generating income from the proceeds of the book that could be considered for proceeds of crime action", suggesting the book's income could be sought for seizure.

Hager's lawyers told the court there were no reasonable grounds for police to seek information without a legal order and questioned whether such an order would have been granted were it applied for.

Lawyers for the police told the High Court the requests were simply the act of asking for information. They said just because police quoted the Privacy Act exception "did not mean the agency was obliged in any way to provide it".

Westpac defended its decision to supply information, saying it followed internal policy in assisting with investigations into serious crimes. It did not supply a copy of the policy despite being asked to do so.

The issue - highlighted in Herald reports - moved the Privacy Commissioner to launch a "transparency project" to see how often law enforcement agencies used the exception.

Media Freedom Committee chairwoman Joanna Norris, editor of the Press in Christchurch, said the work done by journalists was a "safeguard of an open and transparent society".

"I am concerned information of this type was released as a result of this request. The work of journalists should be protected - and the individual rights of any New Zealanders should be protected."

Labour's police spokeswoman, Jacinda Ardern, said it was concerning Westpac provided the information but it was "incredibly concerning" police had sought it.

Police Minister Michael Woodhouse refused to comment. A police spokesman said the agency was "bound by the provisions of the Privacy Act" and was working with the Privacy Commissioner on the transparency reporting project.

• David Fisher gave evidence as an "expert witness" in the Hager v Police case under High Court rules that require an "overriding duty to assist the court impartially on relevant matters".