A blunder by a government worker sent Northland into an 11-day lockdown after travel documents that were meant to be declined were mistakenly approved.

The case of three women who travelled from Auckland to Northland hit headlines in October 2021 - but new documents released under the Official Information Act finally outline the truth behind the saga, and the reason Northland was put into lockdown.

The OIA papers show the women - who had earlier been blamed for using "false information" to get travel permits - had no links to gangs and weren't sex workers, as had been suggested.

Among the documents released is a summary of a police investigation into the women which found "no offence" and no "deception" in obtaining the travel documents.

Detective Inspector Aaron Proctor's summary of "Operation Hiking" quoted an email from the Ministry of Business, Innovation and Employment which said the travel documents were "issued in error by the Ministry of Social Development, (the error not being the fault of the applicant)".

Another document showed it was known three days before the 11-day lockdown was announced on October 8 that human error was behind the travel documents being granted to the women.

One Northland mayor has branded the case "incompetence by the bureaucracy" while another says it would have been "tipping point" for some businesses struggling under Covid-19 lockdowns.

The women were publicly vilified for crossing the border with then Covid-19 Response Minister Chris Hipkins accusing them of using "false information to travel across the border".

The case also saw reporters quizzing Prime Minister Jacinda Ardern over whether the women were prostitutes and former Deputy Prime Minister Winston Peters was forced to apologise for falsely claiming the pair were helped by Hawke's Bay-based Mongrel Mob leader Harry Tam.

The police inquiry summary said: "The police investigation found no evidence to suggest that (the women) had any connection to Harry Tam, the Mongrel Mob or were involved in prostitution."

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The OIA documents set out a timeline that began with an initial application to travel to Northland on September 29 under the "business" category. That application was denied on September 30 because it didn't reach the threshold, the documents show.

A new application was made on October 1 under the "social services" category and was approved.

The paper trail shows police were contacted by a motelier on October 4 who questioned the women's arrival in Northland. The police query coincided with a weak positive result picked up in Whangarei.

The following day - October 5 - police began making inquiries and queries into the women's travel documentation prompted MSD staff to make checks.

Documents released from Hipkins' office showed one MSD staff member emailed another saying: "Have just had a look at this and it should have been declined (approved in error) - I will reopen the case and revoke it."

One of the women returned a strong positive test on October 8 and a snap lockdown was announced that evening to stop the potential spread of the Delta variant. By then, all three women were back in Auckland.

The following Monday the head of MBIE Carolyn Tremain briefed two advisers in Hipkins' office, saying it was MSD's job to monitor compliance of travel permits granted for "social services" and the agency had now brought in a "double-check system".

This led to the October 13 briefing from MBIE to Hipkins, Finance Minister Grant Robertson and Regional Development Minister Stuart Nash. The briefing said: "It is our understanding that the intention was to decline the application but it was approved in error."

Data provided to the ministers showed that business travel documents had been issued for "social services" reasons to 67 businesses with 430 workers.

The bundle of documents released through the OIA showed the extraordinary effort expended by police after the motel owner raised concerns on October 4, two days after the women arrived in Northland.

Police used mobile phone tracking, number plate-tracking cameras and information obtained from banks to track down the women. It also drew in an enormous police resource, including some of the most experienced organised crime detectives in the country, before one, then another woman emerged back in Auckland in self-isolation. They were then transferred to quarantine facilities.

Minister Chris Hipkins said the women had used "false information" to get travel permits. Photo / Marty Melville

The police inquiry established the application came under a valid company name through which one of the women ran a genuine business. It also found a number of business-related phone calls had been made once the women were in Northland.

Proctor wrote: "The fact that (deleted) became ill with Covid soon after crossing the border into Northland is likely the reason for not pursuing the business activities."

His report said, "all became ill with Covid soon after travelling, spent time in their accommodation and returned to Auckland". Information in the OIA showed the women told at least one person they worked in "recruitment".

Far North mayor John Carter said the 11-day restriction compounded the injury Northland experienced being cut off from the country during Auckland's extended lockdown.

"It's another indication of incompetence in our bureaucracy. Unfortunately it's happening too often. Quite honestly, it's not something we can tolerate.

"A good number of businesses were struggling and they won't be happy with that information when it comes out."

Whangārei mayor Sheryl Mai said: "It could have been the tipping point for some businesses. I imagine they will feel pretty annoyed."

Northland Chamber of Commerce president Tim Robinson said its members would be "deeply disappointed" if it emerged the lockdown occurred because of human error.

Robinson said the set of events described by the Herald's OIA documents showed the Government could have "fronted up" about the error at the time.

"Businesses would have been very forgiving if they had just fronted up and said they made a mistake."

In March Hipkins said he had yet to receive any information to suggest he was wrong. He was approached for fresh comment yesterday but has yet to respond. MBIE's Minister Stuart Nash was also yet to respond.

Minister for Social Development Carmel Sepuloni said she was briefed at the time.

"I understand that the information contained in the application wouldn't have met the criteria at the time and it was approved in error.

"I've spoken to MSD officials who are very sorry this occurred. Overall MSD staff assessing business travel register applications for travel across borders during lockdown did a great job, and while this incident was an isolated one, it should not have happened.