The opposition accused the Treasury of being politicised and unprofessional in allowing this ''leak''. In turn, the agency's secretary, Martin Parkinson, denied that his staff gave the costings to anyone outside the government.

And so we dance this farcical dance once more. It happens before every election. I don't know what I'm more fed up with: the confected fury of shadow minister Joe Hockey; the Treasury's dogmatic obstructionism; the hypocrisy of Labor ministers; or even the media, which repeatedly allows itself to be played.

First, however, let's dispel some myths about public service leaks. When people speak of a ''leaked'' government document, it's usually no such thing. A politician, not a bureaucrat, gives the journalist the document, because the politician benefits from the information being made public. Yes, a handful of public servants do leak information without authority, yet the severe penalties for doing so ensure that such acts are very rare. Look no further than former customs officer Allan Kessing, who drew public attention to airport security flaws and received a suspended prison term as his thanks.

But back to Hockey's melodramatics. He inferred that the Treasury leaked the costings - and, in the process, wilfully damaged that agency's reputation - when he knew it was Treasurer Wayne Swan who had slipped them to the media. Hockey also claimed it was improper of the Treasury to analyse policy alternatives. This from a man who spent nine years as a Howard government minister; he must be kidding if he expects us to believe he never asked the bureaucracy to review Labor's policies.

Yet Hockey did make one valid, and important, criticism of the Treasury. With knee-jerk secrecy, it had earlier refused to release its analyses of Greens policies; it even claimed the documents were part of the ''deliberative process'' of government. (Since when were the Greens part of the executive?)

Indeed, even after Swan's office gave the media access to the results of the Coalition policy costings, the Treasury refused to make them public. Parkinson says he must do so, because to breach the Treasury's confidentiality would risk undermining the public's faith in the agency.

Yet that bird has flown. Swan ensured that the costings' findings entered the public domain. By refusing to release all details of its analysis, the Treasury has allowed itself to be abused as a political weapon. Did Swan's office present Treasury's work fairly or selectively? We don't know, because Parkinson won't allow us to check. If the Treasury wanted to uphold its impartiality, it would respond to Swan's actions by publishing its costings in full, thus exposing them to objective scrutiny.

Indeed, this week, Finance Minister Penny Wong said there was a public interest in having policies ''costed and transparent to the Australian people''. And Prime Minister Julia Gillard said she believed ''in an informed public debate'', adding that ''Australians are entitled to know what a policy will cost our nation''.

There is no room to misinterpret those comments. If the Treasury suppresses any costings of policies - whether they belong to the Coalition, the Greens or Labor - it does so against the explicit will of the government. And if the Treasury finds this quandary rather too difficult to cope with, it should have politely referred Swan's inquiries to the Parliamentary Budget Office. After all, that's why the office was set up.

There's a lesson for the media in this, too. During the 2010 election campaign, a similar ''leak'' - which appeared to come from the public service but was, of course, from Swan's office - allowed the Coalition to argue it could not trust the Treasury to cost its policies. Journalists who allow the opposition to get away with this, by not identifying when politicians are the sources of their stories, get in the way of democracy.

Markus Mannheim edits The Public Sector Informant. Send your tips to aps6@canberratimes.com.au