UPDATED 3.39pm: The Prime Minister says he will be able to campaign on tax cuts at the next election - despite only introducing new taxes since the last one.

John Key told Mike Hosking the Government needs a surplus of $3 billion before it can look at tax cuts.

It won't happen next year, but probably will soon after according to Mr Key.

He said philosophically, National believes in tax cuts and smaller government.

"The point is, if we're going to have a tax cut programme, we're not ruling that out for 2017 or campaigning on it for a fourth term, but having probably a bigger one to be blunt."

Labour's finance spokesman Grant Robertson said John Key is irresponsible to raise the prospect of tax cuts.

Mr Robertson said Mr Key was "plucking numbers out of thin air."

“The Prime Minister is being reckless and irresponsible. When people are being forced to live in cars and garages, when older New Zealanders are living in pain because they cannot get operations, we are a long way from being able to afford these kinds of election bribes."

He said tax cuts would put the books back into deficit based on Treasury's forecast of a $1 billion surplus in 2018.

ACT leader David Seymour said waiting until 2018 was leaving it too long.

“Even a $3 billion tax cut in 2018 would barely cancel out the $2.1 billion cost of bracket creep since the last round of tax reforms.  It would be more of a ‘tax reset’ than a tax cut."

Mr Seymour said there's no reason not to bring in a cut now.

"You gotta admire John Key. He's a politician who can simultaneously promise not to cut taxes then promise to cut taxes."

He said issues such as dropping the investment into research and innovation need to be prioritised.

"Today an extra $15 million of corporate welfare, well that's enough to cut the company tax rate by about an eighth of a per cent. That's just one announcement."