The opposition's fearful political interests may have trumped public ones in the infant formula blackmail case.

It comes as the Prime Minister's Office confirms Mr Key has received a number of briefings from the Department of Prime Minister and Cabinet since the blackmail threat was made last November.

Labour MP Damien O'Connor suspects DPMC has taken a leading role in the inquiry and he says its part should only have been technical.

"I'm concerned that those, ones of diplomacy and trade, political considerations by the Prime Minister, may have taken precedence over what risks there really were to consumers."

DPMC is withholding all details in full citing prejudice to national security, international relations and the maintenance of the law - as well as a need to protect confidentiality of advice.

Damien O'Connor says it confirms DPMC has been running the inquiry and process from day one.

He says questions have to be asked if a politically charged organisation should have been leading the investigation, rather than police or the Ministry for Primary Industries.