The National Party have launched an internal inquiry over the recent leak of leader Simon Bridges' expenses.
Leader Simon Bridges told 1 NEWS today the point of the inquiry was to determine if the leaker was from within National.
"It is possible the leaker is a National MP or a staffer, but the point is we don't know. It could be someone within Parliamentary Service or wider within Government."
Mr Bridges said he understood all the MPs were "happy" to be part of the investigation.
"If it's not a National MP or staffer, we may not get to the bottom of it."
He said "appropriate experts" would be used to undertake the investigation.
National MP Gerry Brownlee said in a statement PwC and Simpson Grierson will lead the investigation, funded by the National Leader's Office.
"There will be no further comment until the investigation has been completed."