Back when he was governor, Mervyn King had a line he liked to trot out every time the Bank of England unveiled a new set of forecasts.

The only thing we can be 100 per cent sure of, he’d say, is that there is zero chance these forecasts will be 100 per cent accurate. The wry line was never reported, of course. The following day’s papers would instead be dominated by stark headlines about where the Bank expected inflation or growth to be in the following years.

Similar health warnings can be found in every economic report. They were there in the infamous pre-referendum Treasury analyses that erroneously forecast a recession if we voted to leave the EU. They are beneath every set of International