Claims the Coalition's income tax cuts will produce an economic boost have been met with scepticism by a former adviser to John Howard, as well as ratings agency S&P, which has warned the credit outlook remains on negative outlook "for now" because of growing global risks.

While the budget position has benefited from stronger revenue flows, Scott Morrison's economic outlook is too rosy and leaves the nation vulnerable to a sudden downturn, said Peter Crone, chief economist at EY.