Claire Trevett: PM cannot afford to let Budget 'leak' slide

National Party leader Simon Bridges. Photo / Mark Mitchell

The biggest story of the release by the National Party of Budget details is not the information in it, but the fact of the release itself.

The Budget is one of the most sensitive and tightly controlled stores of information a Government has.

While successive governments have taken to releasing individual funding announcements ahead of the Budget to eke out the publicity, it always has control of what information is released and what is not.

Any loss of that control is a scandal and cannot simply be ignored.

The most controversial "leak" in recent times was the 2006 Budget leak of plans to unbundle Telecom – plans that were highly market sensitive.

An inquiry found a Parliamentary messenger had passed on the information to a mate in his cycling team, who was an employee of Telecom.

Prior to that in 1986 then Finance Minister Roger Douglas offered his resignation after staff accidentally issued Budget documents early.

This release is not of the same scale as either of those.

But the scope of the information was wide, covering the "vote overviews" (the summary of spending) of 18 out of 40 areas of spending.

Finance Minister Grant Robertson was quick to downplay it, saying it did not provide spoilers of the new spending initiatives planned by the Government, was not overly sensitive, and some numbers – but not all – were incorrect.

That may be, but the Government and Treasury need to find out how it got to Bridges.

There are many possibilities, from a mole in Treasury to a hapless mistake.

Bridges was careful to say it was not necessarily a "leak". National had not released the information in its original format, but rather adapted last year's documents to include the new figures.

A leak is usually a deliberate release by a source (this time either within the Treasury or the Government), usually with ill intent.

Alternatives to that include human frailty – the information could have been left behind somewhere.

It could have been hacked from Treasury, or Treasury could have blundered and accidentally put up the information on the website pages it has already set up ready to go live on Budget Day.

A look at the Treasury website showed that the areas of spending for which "vote overview" pages were already prepared to go live on Budget Day were exactly the same as those National released, with just one exception.

Others – such as education – were not yet on the website and not included in the National Party release.

Treasury is now investigating. If it was a blunder at Treasury it is bad news indeed for the person who made that blunder.

But it would be good news for the Government. The alternative is that somebody had deliberately released information to the Opposition.

That cannot simply be waved away.

This is not the first information release to hit the Government.

Early in May, the National Party received a leak and released the Cabinet paper on plans for a cannabis referendum before Cabinet had even decided on it.

At the time Ardern said it was not worth spending much time or energy on hunting down that leak.

But she was very careful not to completely rule out having a quick look to see where it came from, although it was interpreted that way by many. Cabinet papers are as sensitive as Budget documents.

Sure enough, after that her office asked chief executives to make sure staff with access to the paper had handled it appropriately. That process is underway.

What Ardern would be wary of is a full inquiry of the kind former Prime Minister Sir John Key called into the leak of a review of the GCSB spy agency to Stuff's Andrea Vance in 2013.

That inquiry gave Key – and others – more headaches than it was worth.

Ardern may have been wise to avoid a similar situation. But this time – unless there is a confession of a blunder - she cannot afford to take the easy way.