A bout of global stock-market turmoil and an outbreak of UK street violence as adjacent news items gave an apocalyptic feel to the start of the week. But as rioting continued, markets appeared to steady, led by Tokyo with a 10 per cent Tuesday rebound. We know the ugly sentiments that animate the thugs – but do we understand the sudden nerviness of investors?

Once media clamour about 1,000-point falls subsided, two strands emerged, both American.