As markets trembled on Thursday, Standard & Poor’s, the US rating agency, detonated another small grenade. After announcing in March that it expected banks to write off $285bn of mortgage assets, it casually raised that estimate by $100bn-odd, owing to falling asset values.

Compared with recent dramas, that $100bn might not look so disastrous (Nouriel Roubini, the American economist, expects $2,000bn total credit losses before the end.)