A roadblock set up by New Zealand police to obtain information on euthanasia activists was illegal and unjustified, an investigation has found.

In late 2016, members of pro-euthanasia group Exit International were stopped by police at a roadblock after leaving a meeting. They were asked for their names and addresses, before being breathalyzed.

Later, 10 of the women who were stopped at the roadblock were visited by police in their homes.

Several members of the group – who were mostly in their 70s – were also visited by police in other parts of the country, in what Exit International believed was a targeted police campaign.

The New Zealand Independent Police Conduct Authority (IPCA) has concluded that officers used the roadblock to obtain information unlawfully on Exit International members, and were “not justified” in doing so.

Police were monitoring the Exit International meeting in Lower Hutt as part of an investigation into the death of a woman who ingested pentobarbitone – a controlled drug that is designed to peacefully euthanise animals.

During the meeting officers overheard people discussing how to import euthanasia drugs. They immediately set up a roadblock, saying they feared some attendees might be at imminent risk of harm.

“Police should have recognised that they had no power to stop vehicles in these circumstances,” said IPCA chair, Judge Colin Doherty.

“It was an illegitimate use of police power that unlawfully restricted the right of citizens to freedom of movement.”

However, the subsequent welfare checks on members in their homes were not illegal, the IPCA found, and stemmed from genuine concerns held by police.

“The authority acknowledges that the welfare support visits generated stress and apprehension among some of those visited,” said Doherty.

“But they were well intentioned and generated by a genuine concern for the wellbeing of those visited. There is no evidence that the visits were intended or used for any investigative purpose.”

Exit International’s Philip Nitschke said the New Zealand police acted in a “subversive and dishonest manner” and called the targeting of members “unthinkable”.

He added: “Wellington is not Moscow and the NZ police are not the KGB. Such underhand and downright dishonest tactics have no place in New Zealand civil society.”

Assistant Commissioner Bill Searle said police accepted the findings of the IPCA report and took no moral position on the issue of euthanasia.

“We accept that establishing a vehicle checkpoint to identify meeting attendees was unlawful. However, our staff acted in order to protect life and did not intentionally break the law.”

In Australia, the crisis support service Lifeline is on 13 11 14. In the US, the National Suicide Prevention Hotline is 1-800-273-8255. In the UK, the Samaritans can be contacted on 116 123. Hotlines in other countries can be found here.