Labor will not set aside additional long-term funding for hospitals despite its promise to provide decade-long costings and its sustained attack against the Coalition for cutting $57bn from projected spending on hospitals over that timeframe.

Over the weekend Labor promised an extra $2bn for hospitals over the next four years – on top of the $2.9bn being offered by the Coalition – an amount it insists can revive a funding agreement with the states that was scrapped under Tony Abbott.

Labor sources suggested the longer term funding arrangements would be clear when the ALP releases its promised 10-year costing details later in the election campaign.

But on Monday Labor clarified its long-term costings would not contain any provision or contingency for extra money for hospitals – beyond the current four year deal – because a longer-term agreement would have to be negotiated with the states, whichever party won on 2 July.

“Once we negotiate a new agreement – and that’s the same logic my opponents are using – then you can accurately forecast what the expenditure will be,” the Labor leader, Bill Shorten, said.

“I’m optimistic that because we’re spending this extra resource on hospitals now we may not need to spend as much as maybe forecast in the future because what we’re about is the contributing to the 50% efficient price of hospitals. We’ve seen in the previous agreement when Labor was in power that we’ve seen reforms which actually put downward pressure on the cost of running our hospitals.”

Experts concede that even rough estimates of the commonwealth share of a future hospitals agreement are difficult, but Labor is presenting the 10-year costings as proof of its economic credentials and its capacity to balance the budget, so omitting any provision for extra hospital funding will also raise questions about the costings’ accuracy.

The former Labor government had promised the state’s $57bn in long-term hospital funding after protracted negotiations to address the fact that the cost of hospitals – as the population aged and medical technologies became more expensive – was projected to exceed some states’ entire budgets over time. The Abbott government cut this agreement in its 2014 budget, slicing $57bn from projected forward spending.

All states insisted they could not possibly operate existing hospitals with that funding, declaring the situation a “crisis”. The New South Wales premier, Mike Baird, calculated the shortfall would reach $35bn nationally by 2030.

At the Council of Australian Governments meeting in April, the prime minister, Malcolm Turnbull, offered the states an interim $2.9bn over the next three years, to give time to negotiate a new long term federal/state agreement.

Labor has now pledged to add $2bn to that deal. But unlike its promise to restore over $30bn in schools funding over the next 10 years, an amount also cut in the 2014 Abbott budget, it is making no specific long-term pledges regarding hospitals.

The health program director at the Grattan Institute, Stephen Duckett, said hospital funding was uncertain under both parties.

“Both parties should be offering ongoing funding, the whole idea of having these stop start agreements creates uncertainty,” he said.

Duckett confirmed that the estimated increase in costs had fallen well below $57bn, but said no specific figures were available.

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