In a bleak report ahead of the Budget in November, the Office for National Statistics revealed the Government borrowed £18billion last month alone as it spent more on the state than it raised in tax.

Allan Monks, UK economist at JPMorgan, told the Financial Times that even shaving 0.1 or 0.2 per cent from productivity would leave a hole of between £9billion and £18billion.

The Treasury has borrowed more than forecast so far this year, official figures show, raising pressure on Rachel Reeves as she seeks to fill a gaping hole in the public finances.