One conclusion from covering many Budgets is that forecasting is more an art than a science. The Treasury has been frequently way off course in their economic predictions. Take public sector net debt. For the year 2015/16 the Treasury predicted in March 2011 it would be 71% of GDP, in 2012 76% and in December 2012 almost 80%. It turned out to be 83.6% (and is currently 87%).

A difference of some 12% of GDP in forecasts, equivalent to billions of pounds, must play havoc with any public spending planning.