Criticism of Treasury head for lunch costings 'rubbish'

What started as a debate over the cost of lunch has devolved into accusations of dishonesty and a breach of the public service code of conduct.

Shadow treasurer Angus Taylor charged the government with an "egregious politicisation of the public service" after it released analysis provided by Treasury showing a coalition policy to allow small businesses to write off lunches on tax would cost $1.6 billion per year.

That forced the hand of the opposition, who revealed their own analysis, produced by the independent Parliamentary Budget Office (PBO), costed it at less than $250 million.

Treasury secretary Steven Kennedy needed to provide a "full explanation" as to how it came about, Mr Taylor protested.

"We have a long-standing custom in this country of not politicising the public service," he told reporters on Tuesday.

"But it is very clear today, the treasurer is intent on doing exactly that."

The PBO was set up in 2012 to provide non-partisan analysis of policy, in part to prevent the risk of governments weaponising Treasury to discredit opposition proposals.

Mr Taylor argued the parameters the government provided Treasury were different to those assumed by the coalition, thereby providing a dishonest representation of the policy.

"Steven Kennedy will need to answer why he has done this and how this is not a breach of the Australian Public Service Code of Conduct," he told Sky News.

Public servants being accused of contravening their obligations to objectivity was nothing new, said former Treasury secretary Ken Henry.

"If the Treasury secretary is requested to do a piece of work for the government, and it's lawful, then the Treasury secretary should do it," he told AAP.

"I was frequently accused of having engaged in some activity which was seen as being political, rather than a piece of dispassionate analysis.

"But it's all rubbish. It's just part of the way that political debate is conducted in Australia and ,unfortunately, I don't think we're going to change it."

Dr Chalmers said the government had a duty to provide Treasury's costings to the Australian people because the coalition had not been forthcoming with their own figures, despite announcing the policy two weeks earlier.

"I heard Angus Taylor was losing it this morning on TV," he said.

"To be frank with you I would rather not have to do it. I would rather a responsible opposition provided the costings of their policy and told Australians what they were going to pay for it. That hasn't happened.

"Part of my job is to understand risks to the budget, and this is a very substantial risk to the budget."