Twenty years ago on Friday, traders in New York arrived for the start of the working week in a worried frame of mind. Wall Street stocks had shed more than 5 per cent the previous Friday, leaving them with a weekend to ponder where the market would go from there.

Before their day’s dealings began, they heard news that Hong Kong’s stock exchange had fallen more than 5 per cent. More dramatically, prices on the London Stock Exchange, in part still reacting to the effects of a hurricane that had hit southern England at the end of the week before, were down almost 10 per cent. There was little other news but international tensions were rising, with some sabre-rattling between the US and Iran.