National's Budget 2019 drops could be the Government's greatest crisis

A witch-hunt is underway at Treasury to find out who's responsible for top secret Budget details falling into the hands of the National Party two days before the Budget's release.

Budget breaches are extremely rare and when it's happened before, Finance Ministers have offered their resignations to the Prime Minister - but not this time.

National released details of how much money 19 Ministries will get in the next year, including foreign affairs, defence and forestry.

"The Government has money for tanks but not for teachers," National leader Simon Bridges said, referring to the $1.3 billion that National claims will be spent on defence next year.

"It's not the Wellbeing Budget - it's the Winston [Peters] Budget."

The Government confirmed some of the Budget details were accurate. 

"There are some numbers that are right some numbers that are wrong," Finance Minister Grant Robertson said on Tuesday.

When asked how much of it was correct, he said: "You'll see on Thursday."

The Government says there's no way the breach came from the Beehive because that information doesn't go to Ministers, and Bridges has refused to say where the information came from.

The Government says the only people who had access are the Treasury, the printers of the Budget, the Parliamentary Council Office which deals with Budget legislation, and the office of the Auditor General.

The chief suspect is the Treasury, the Government's bookkeepers which put together the Budget.

In a phenomenal move, the Prime Minister refused to express her confidence in Treasury two days out from the Budget.

When asked if she had confidence in Treasury, she said: "As I say, we haven't looked into this in any great detail yet."

And the Finance Minister's trust is wavering.

"This is something we'll now investigate to see if that confidence is maintained," Robertson said.

When asked if heads will roll because of the information being released, he said: "That's all for after Thursday."

In 1986, when Budget details were released pre-Budget, then-Finance Minister Roger Douglas offered his resignation.

Robertson said he's not intending to do that: "The world has changed a lot since the 1980s."

National got the last laugh, when Deputy Leader Paula Bennett asked to seek leave in Parliament for Bridges to answer questions about what was coming out of the Budget.

Beyond matters of national security, the Budget is the Government's most closely guarded secret.

The Treasury is frantically reviewing everything right now - whether these details were accidentally sent to National, erroneously uploaded somewhere whether there's a leak.

Any of those options are extremely serious. This is probably the greatest political crisis this Government's faced to date.