Public sector spending was £18billion higher than income in August despite surging tax revenues.

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.