The federal government says restoring the building industry watchdog will boost productivity but the size of any actual benefit to the economy is difficult to know - a fact noted by the Productivity Commission itself.

As the government moves to re-establish the controversial Australian Building and Construction Commission (ABCC), ministers including Employment Minister Michaelia Cash have said it will boost productivity in the industry. However, trade unions royal commissioner Dyson Heydon noted in his final report, delivered in December, that the impact of the watchdog…