Prime Minister Bill English says his ministers should not have been told about Winston Peters' superannuation overpayments. However, he does not believe the leak came from within the Beehive or the National Party.
English said he was concerned about how the matter became public and he would take any leak "very seriously".
"I have no tolerance for leaks of this nature. Mr Peters is understandably concerned about how the matter became public and so am I."
He said Ministerial Services would look at how the information was handled within the Beehive.
He said it was up to the chief executives of Government departments to decide what should be notified under the "no surprises" policy.