Treasurer Joe Hockey and Assistant Treasurer Josh Frydenberg have hit back at Peter Costello after the former treasurer criticised the Liberal government for failing to live up to its promise of delivering a "fairer, simpler tax system".
The government ministers said they could only dream of having the revenue he had at his disposal during the Howard government.
Mr Costello, whose mining boom expenditure plunged the budget into structural deficit with tens of billion of dollars committed to tax cuts and middle-class welfare measures which can no longer be funded, has rounded on the Abbott government for its penchant for increasing taxes.
In his regular column for the News Ltd tabloids, Mr Costello describes the Abbott government's pledge of "lower, simpler, fairer" taxes as some kind of "morbid joke".