Prime Minister Bill English fought to have his police statement over the Todd Barclay affair withheld from the public despite arguing in Parliament it was a police decision to keep his involvement secret.
Documents released under the Official Information Act show police believe English's statement should have been released.
But all mention of English was removed from the file when it was released to the Herald in March.
It later emerged the Prime Minister had been interviewed as a witness in the police investigation into allegations Barclay secretly recorded a staff member, raising questions over how his involvement had been hidden from the public.
English distanced himself, saying the decision was one for police. He told Parliament he was aware an OIA process was underway but he did not really take part in it.
"I am sure that all discussions were conducted consistent with the Official Information Act, and the police, in the end, have statutory independence. In addition to that, like any other agency, it makes the decisions about what information it releases, taking into account whatever factors it thinks are relevant."
The new OIA documents show an advocate for English pushed hard - successfully - to have the Prime Minister's involvement scrubbed from the file.
Police wrote to the advocate - likely a staff member in the Prime Minister's office - to ask if English was comfortable having his statement released, along with a text message that had been taken as evidence.
The text message was between English and former Southland electorate chairman Stuart Davie, who later spoke out publicly with his concerns about Barclay and allegations the MP had secretly recorded staff member Glenys Dickson.
"We have very serious concerns that a private text conversation between Mr English and Mr Davie is proposed to be released."
Police were told it should be withheld on privacy grounds as it was a text message "between two private individuals".
"The text communication involved Mr English as a member of the National Party, communicating with another member of the National Party."
Police responded after taking legal advice, saying it had removed some details but could not "justifiably withhold the entire text or make any more redactions based on the grounds you have listed".
Police were then told that if the text message was removed, then all mention of the text message should be removed from English's statement - if it was released at all.
The release of the OIA was postponed and after repeated requests on behalf of English, police said the Prime Minister's witness statement would be withheld along with any text messages.
Canterbury crime prevention manager Inspector Tony Hill - who was handling it for police - then asked: "Were there are other areas of concern?"
English's advocate asked: "Can you please clarify if there is any reference to Mr English in any other material being released?"
When told a statement would be made saying English had been interviewed, the advocate asked: "Can you explain why the only person who can be identified from this summary is Mr English?
"No other person involved in the investigation is able to be identified - why only Mr English? Instead of categorising people, why don't you refer to witnesses as interested parties?"
The information was released shortly after with no reference to the Prime Minister.
Police faced questions when it emerged English had been interviewed and released a statement which said "police consulted those individuals who provided statements as part of the investigation. The redacted file that was released took into account the views of the individuals consulted."
English released the statement when it was revealed he had been interviewed, showing he had been drawn into the allegations of secret recording.
No charges were laid against Barclay, who is not standing for re-election.
A spokeswoman for the Prime Minister said last night:
"As we have previously stated, yes the Police contacted Mr English about releasing his statement and text messages.
"A staff member in the National Party Leader's Office advised them that whether or not Mr English's statement was released was a decision for Police.
"Because the text messages were private, and not sent in his ministerial capacity, it was suggested they should not be released publicly. The final decision on whether to release the text messages was a matter for the Police."