Prime Minister Malcolm Turnbull and Treasurer Scott Morrison have rejected claims that Australia's triple-A credit rating is at risk, despite the head of Treasury warning Australia cannot afford to be complacent about its fiscal position. 
Treasury Secretary John Fraser used his first public speech for 2016 this week to warn that spending on federal government programs - such as the National Disability Insurance Scheme - will be ramping up in coming years without an equal rise in revenues to pay for them.
He said the Commonwealth budget was under serious pressure, with real spending growing at an annual average rate of around 3.5 per cent since 2007, compared with around 3 per cent during the 1980s and 1990s.
He used his speech to return attention to the budget's structural imbalance, saying the government was not collecting the revenue it needed to pay for the projected growth in Commonwealth spending over the next decade.
He then warned that Australia could not become complacent about its fiscal position.
"[Our] historically low nominal growth outcomes and lower growth projections, alongside historically high payments-to-GDP, mean that it's taking longer for the budget position to return to pre-crisis levels compared with the cyclical downturns of the early 1980s and 1990s," Mr Fraser told the Sydney Institute.
"It's important that Australia maintain its top credit ratings, which helps to contain the costs associated with servicing public debt.
"Australia is one of only 10 countries with a triple-A credit rating from all three of the major rating agencies, reflecting our reputation for fiscal prudence ... We should not be complacent about this. I know from personal experience during the financial crisis how important a strong credit rating is to investor confidence," he said.
But Prime Minister Turnbull rejected any assertion on Friday that Australia's triple-A credit rating was under threat.
He said international ratings agencies had given a "very positive review of the government's strategy to move back into fiscal balance" as recently as the   December mid-year budget update.
Treasurer Scott Morrison also criticised the suggestion that Australia's credit rating was under threat, saying the government had a plan to reduce spending.
"Our plan is to reduce expenditure as a share of the economy from 25.9 per cent to 25.3 per cent," Mr Morrison said. 
"We are actually reducing spending as a share of the economy as the Treasury secretary acknowledged last night. So the path of fiscal consolidation is well and truly being followed by this government."
Economist Chris Richardson, from Deloitte Access Economics, said rather than emphasising Australia's credit rating, we ought to be talking about the eventual costs of servicing our national debt, because when interest rates finally start increasing from their historically-low levels we will need to be prepared to pay much more in interest costs.
Private economist Saul Eslake said Mr Fraser's speech was important because it has put budget repair back on the agenda.
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