Five weeks out from the budget the head of the Treasury has called for a "fundamental rethink" of the links between superannuation, pensions, housing and the welfare system.

John Fraser told a conference about Australia's intergenerational challenges that in the 25 years since he and his colleagues helped set up Australia's superannuation system it had become clear they got some things wrong.

"We are pretty smart but we are not smart enough": Secretary of Treasury John Fraser. Credit:Alex Ellinghausen

"We are not smart enough in Treasury – we are pretty smart but we are not smart enough – to model third, fourth and fifth rounds of reactions to policy measures," he said.

"I think the time has come 25 years or so after those big reforms to have a more fundamental rethink about the interaction between superannuation and tax and the whole welfare system."