As economists geared up to analyse the Federal Reserve’s interest rate decision on Tuesday, their attention was grabbed by an unusually worrying indicator on the health of US exports.

The Institute for Supply Management’s index of new export orders in the services sector dropped by 4.5 percentage points in July, slipping to a five-month low of 47.5 per cent. Last Friday, a similar ISM index for manufacturers also fell by 4.5 percentage points, to a reading of 54 per cent – the lowest since last December.