The Green Party says voters shouldn't have to guess who's numbers are right, as it pushes for a Parliamentary Budget Office.

It says parties are already accusing each other of fiscal holes this year - highlighting the need for an independent office to cost election policies.

The party's written to Finance Minister Nicola Willis and Labour's Barbara Edmonds, urging support.

Green Party co-leader Chlöe Swarbrick says there's demand for this on both sides of the political aisle.

"Wouldn't it be useful to have an independent body that can say - hey look very clearly here, if we compare apples with apples in terms of uniform forecasting protocols, then this is demonstrably untrue. That would mean political parties would also tighten up their act."

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