"The way it was told to me, they didn't have any details, it was just rumour, and they were just gossiping to each other. Penny Webster then took that up with Len Brown," Mr Key said today.
He said it did not amount to a tip-off aimed at forewarning Mr Brown's team and even if it had, he would not have had an issue with it: "We've got nothing against Len Brown."
He maintained the National Party was not involved.
"I don't have any advice and I don't believe the National Party has been involved at all. There may be people who knew about it who are members of the National Party, or at least vague sort of details, but there are also many people who knew about it that weren't members of the National Party."
A source inside the Brown camp had also told the Herald that Ms Webster alerted them to the tip after hearing it from Mr Mitchell.
Ms Webster - a former Act MP and loyal supporter of Mr Brown, yesterday would neither confirm or deny passing on the tip to the Brown campaign when approached by the Herald.
Mr Mitchell didn't know Whaleoil was working on the story and had heard only vague rumours about Mr Brown.