Police have spoken to thousands of people since the 1080 infant formula blackmail threat and say today's "deadline" is no reason to change tactics.

This evening, police deputy commissioner Mike Clement elaborated on the vast logistical and information-gathering effort behind Operation Concord.

Anonymous letters sent to Fonterra and Federated Farmers in November said formula would be laced with 1080 if New Zealand didn't stop using the poison for pest control by the end of March.

Police launched Concord in response.

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The deputy commissioner said police had visited more than 3500 dairies, supermarkets, pharmacies and service stations to discuss issues including how to safeguard formula from tampering.

Mr Clement said police had now investigated more than 70 reports from the public about infant formula having possibly been tampered with, and in each case tests later ruled out the presence of 1080.

A further 600-odd calls came from people offering information or tips. "The vast majority of these are people who think they can help."

Mr Clement said police had greatly improved their knowledge of 1080 during Operation Concord, and he thanked people who had shared their expertise on the toxin and its uses.

"Police didn't come into this investigation as experts on 1080."

He said a "core group" of 35 investigators was based in Auckland, but an "awful lot more" officers nationwide had carried out the 3500-odd visits to retailers.

Details of these visits were being collated in a database.

Concord was comparable to the biggest police operations in recent history, Mr Clement said.

Nobody has been arrested over the threat, which anti-1080 campaigners have condemned and the Prime Minister called an "eco-terrorist" outrage.

Mr Clement said the "deadline" would not force a change in police tactics, and the public should not be unsettled either.

"Nothing changes in essence because we've [taken] the investigation seriously from the outset and we're continuing to do so," he said.

He said Concord was based on well-established investigative methods and there was no immediate need for those methods to change.

There were no starkly obvious precedents for Concord but police had spoken to people who had made similar threats before.

"Every now and then, people do get pushed over the edge for one reason or the other ... some people have gone beyond what's acceptable," Mr Clement said.

Yet the deputy commissioner said there was universal revulsion at the blackmail attempt -- and no anti-1080 campaigners had shown any sympathy for the threat to poison babies.

Mr Clement said police were working with all groups of people involved in 1080 distribution or testing to see if missing or stolen poison was relevant to the investigation. But he said it was counter-productive to speculate on the origin of the poison powder used in the November letters.

Mr Clement said advice from police to the public was unchanged.

"I would just say to people, if you think you have got some information ... it's best for us to make the judgement call."

WHO TO CONTACT

If you have any questions about what to feed your baby, call Plunketline 0800 933 922 or Healthline 0800 611 116

For more information go to foodprotection.govt.nz

Police say people are welcome to contact them anytime if they have information possibly of use to the investigation.