A few years ago the then Treasury secretary and I were discussing Malcolm Turnbull’s plan to increase the GST to 15 per cent and cut income taxes. He told me the Treasury economic model showed that such a controversial change to the tax system would have a negligible effect on the nation’s GDP.

You can understand why Turnbull dropped the plan. When the Treasury’s model was publicised it would have been ridiculed by opponents of the plan, not least the opposition. The Treasury model would have been devastating evidence in the court of public opinion.