Prime Minister John Key has given his "100 per cent" assurance that intelligence agencies were not spying on Winston Peters, indicating his source was controversial blogger Cameron Slater.



Key revealed today that he speaks regularly with Slater.



The blogger runs the Right-wing attack blog Whale Oil and was recently under fire for branding a West Coast man who died in a car accident a "feral".



Key was responding to NZ First leader Winston Peters who had said the only way Key could have known Peters had visited Kim Dotcom three times was if Peters was being spied upon.



Key rejected the accusation today.



"I can absolutely swear my life on it, that there's been no public agency [involved]," he said.



Such a move would spell "the end" of his time as prime minister and of his government. Peters was "out to lunch and in La La land," Key said.



"Contrary to what you might want to believe I can read, it happened to be in the New Zealand Herald, it happened to be on the Whale Oil website, and a member of the public, basically for want of a better term, rang me up and said what was the case," Key said.



"I assumed it was right, I said it and it turned out to be right."



He confirmed he and Slater spoke regularly, including this week when they discussed Dotcom, but Key hedged when asked if Slater was his source.



"I wouldn't say that ... I wouldn't say either way, I'm just telling you it's not GCSB or SIS."



Key said he regularly called Slater, who broke the story of the Len Brown affair, "to see what he's got on his site and mind".



Key's office has long been rumoured to be linked to the blog.



One senior staff member was caught last year sending photos of the aftermath of the press gallery Christmas Party, but Key has never confirmed the relationship.



Key said he was not deterred by the controversy around Slater, who last month received death threats for calling a man who died in a car accident a "feral".



Key said Slater was a blogger who wrote on a variety of topics, which he did not always agree with.



Slater confirmed he was the source.



"If the prime minister said that's the case, that's the case," Slater said.



Controversies surrounding Slater should not preclude the pair from having a professional relationship, Slater said.



"I've got a wide network that's got across the party spectrum. I've got contacts in the Labour Party, I've got contacts in the Green Party, I've got contacts in the Conservatives, I've got insiders in NZ First, I talk to everybody."



He described his relationship with Key as "professional ... where I ask questions and he gives me answers".



"I wouldn't say that I'm a mate of his, I've never been to his house, nothing like that. I'd just say that it is what it is."



Slater also criticised Peters for not coming clean about the visits earlier, with the NZ First leader saying Dotcom had originally asked him to keep the meetings confidential.



"I just want Winston for once in his life to start telling the truth ... He's been caught red-handed," Slater said.



Other MPs had visited Dotcom "and they need to start fessing up – there's been dodgy deals going on", he said.