Patrick Gower believes the National Party is "bluffing and blustering" after announcing its tax cuts plan last week.
National's leader Christopher Luxon has been fending off criticism of the plan, with Labour claiming it doesn't "add up".
National wants to give $14.6 billion in tax relief to the "squeezed middle", largely funded through several new revenue streams including partially lifting the ban on foreign buyers while slapping them with a tax, as well as offshore online gambling and user-pays immigration levies.
According to Labour and some experts, however, the foreign buyers' tax wouldn't raise enough revenue and could break international law. Meanwhile, Newshub revealed on Tuesday it would be illegal to license new online gambling operations and required a law change.
Gower, a Newshub journalist and former political editor who spent a decade in the Beehive, said National's plan was "quite a lot of jiggery pokery".
However, National finance spokesperson Nicola Willis "might get away with" the plan, according to Gower.
National was "just going to bluff and bluster their way through their jiggery pokery and hope that Kiwis don't understand and don't care", Gower said.
"I tell you what their tactic is, it's: 'Keep going... we'll just say we're going to do it and we reckon we will just get through'."
According to Gower, speaking on AM's Wednesday panel, more public service jobs would be in the firing line if not enough revenue was raised.
"If you want to put those tax cuts through, and they can't get their money out of the 'jiggery pokery'… borrowing will be terrible for inflation so it might be those bureaucrats in Wellington," he said. "There might be a few more of them on the train to the Wairarapa to retire."
Luxon, earlier on Wednesday, dismissed claims the numbers in National's plan didn't add up.
"It absolutely stacks up and you should know that [National finance spokesperson] Nicola Willis and I are good with numbers and good on economics, and it's in good shape," he told AM.
"The important thing here is, what we're doing is we're raising revenue, reprioritising spending and giving money back to hard-working Kiwis - what we call the 'squeezed middle.'
"We're very confident all of that is completely doable."
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