Treasury boss Tim Marney was forced last night to wade into the political row over public transport costings, declaring he would stake his career on the independence of his department.
Labor leader Mark McGowan said yesterday he would refuse to submit Labor's Metronet public transport plan to be costed by Treasury because he did not trust Treasurer Troy Buswell not to interfere in the process.
Labor's ire was stoked when an official from Mr Buswell's office was at a Treasury briefing last week for Labor MPs Ben Wyatt, Ken Travers and Rita Saffioti.
Labor claims it did not know the ministerial staffer was present and has used it to accuse Mr Buswell of political interference.
"I honestly do not trust them not to doctor anything produced by Treasury," Mr McGowan said.
"The people in Treasury are good people but the problem is Mr Buswell and Mr Barnett's behaviour."
Mr Marney said: "The caretaker conventions explicitly state that Mr McGowan's request for costings is to be addressed directly to me.
"All correspondence will be direct between myself and the Opposition and at no point will that be shared with the Government.
"There is no opportunity for involvement or interference by the Treasurer's office whatsoever.
"I would, of course, stake my job on that remaining the case."
Labor says its Metronet plan will cost $3.8 billion but Mr Buswell has insisted the true cost is $6.4 billion, based on costings he has variously attributed to the Public Transport Authority and Treasury.
Seeking to clarify Treasury's role, Mr Marney said: "Cost estimates for a series of projects similar in nature but not exactly the same as Metronet were sought from the PTA and passed to the Treasurer's office prior to the caretaker period being enacted."
He said Treasury had not had time to independently verify the PTA costings.
Mr Marney said he regretted that he did not make clear that a member of Mr Buswell's ministerial staff was at the Treasury briefing.
"I regret deeply not being clearer at the outset of the meeting," he said.
"However, the briefing was requested by the Treasurer's office and I had assumed that in correspondence between the Treasurer and shadow treasurer that the Treasurer's office had made it clear they required a representative at that meeting."