More than one million older Australians will be caught up in changes to private health insurance rebates as the Albanese Government faces questions over whether it has dramatically underestimated how many people could dump their cover.

Government modelling suggests about 44,000 older Australians will drop their private health insurance following the changes, but Medibank reportedly puts the figure at 91,000 — more than double the official estimate.

About 1.2 million older Australians are expected to be affected by the policy, while four states are reportedly demanding Labor reconsider the changes amid concerns already stretched public hospitals could face additional pressure.

Employment Minister Amanda Rishworth was grilled over the numbers on Sunrise on Wednesday, and was forced to defend the Government’s modelling while describing the measure as a “difficult decision”.

“Well, firstly, if we think about this decision, it was a difficult decision, but an important decision. And the reason for that is that we need to be very resourceful with where we spend taxpayers money,” she said.

Ms Rishworth also pushed back on suggestions Labor was completely scrapping the private health insurance rebate for older Australians.

“We’re not scrapping a rebate. Older Australians and younger Australians still have access to a rebate based on their income, and still can get a maximum of 24 per cent rebate.”

The change instead removes an additional age-based component of the rebate.

Pressed on how much individual pensioners could be left paying, Ms Rishworth said costs varied depending on their policy but maintained the Government expected only a “modest impact” on private health participation.

The Minister argued the savings were necessary as the Government grapples with soaring demand for aged care, pointing to an additional $3 billion allocated for more home care packages.

Nationals Senate Leader Bridget McKenzie seized on the figures, warning the changes could simply shift pressure onto the public health system.

“I don’t think it should be a trade off between home care packages for older Australians and private health insurance for older Australians,” she said.

Ms McKenzie claimed Labor had failed to properly account for the consequences and warned older Australians who had maintained private insurance for decades could ultimately abandon it.

“Only to find a government ripping out the rug under them. And premiers today are furious. Even Amanda’s own Premier, because they’re going to all flood into the public system now and clog up waiting lists. That’s literally what’s going to happen.”

Ms Rishworth rejected suggestions the necessary work had not been done, saying Government estimates indicated the policy would have a limited effect.

“What we’re saying is this will have a modest impact on those that drop out about 0.4 per cent. And we still expect to see private health insurance take up continue.”

The dispute now centres on just how “modest” that impact will be, with the Government and Australia’s largest private health insurer offering sharply different predictions.