John Key was approached by police about his claimed knowledge of the identity of the hacker "Rawshark" but won't say if he cooperated.

The approach came after the Prime Minister said publicly he had been given the name of a person who was said to be the hacker Rawshark.

A spokeswoman for the Prime Minister said: "Police gave the Prime Minister the opportunity to provide any relevant information. The Prime Minister indicated his suspicions on the identity of Rawshark were based on hearsay."

But she would not say whether Mr Key had spoken to police or passed on the "hearsay" information to police.

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When it emerged after the election that Mr Key had been told the identity of a person who was believed to be Rawshark, he said he would not pass it on to police.

"In the end if the individual who told me wants to tell the police they are welcome to do that," Mr Key said at a media conference at the time.

The question of Mr Key's knowledge became public after a a new chapter in the book John Key: Portrait of a Prime Minister quoted Mr Key saying: "Someone phoned and told me who the hacker was, but other than having a look at this person, I thought, 'Oh well ... nothing will come of it. Life goes on'."

The Prime Minister's knowledge of the identity of the hacker was a feature in documents released from a High Court file in which journalist Nicky Hager is challenging police efforts to search his house to find the identity of Rawshark.

Rawshark was a central figure in last year's election drama after he claimed to have hacked the computer of blogger Cameron Slater, passing the information to journalist Nicky Hager who used it to write the book Dirty Politics. The book purported to show an alliance between the National Party and elements in the blogosphere.

After publication, a police investigation was launched into the hacking of the computer which led to a search warrant executed on Nicky Hager's home. In a court case challenging the search warrant, Hager's lawyers claimed police hadn't exhausted investigative avenues, which they were obliged to before creating a situation which put a journalist's source protection in jeopardy. Hager has challenged the search warrant used by police to search his home. A judgment is expected from the High Court shortly.