Et tu, Martin? Not since 44BC, when Julius Caesar donned his toga for an ill-fated stroll down to the senate, has March brought such bad news for strong leaders.

Sir Martin Sorrell of WPP on Friday joined the ranks of British chief executives who might profitably have skipped last month. By highlighting in its trading statement the “somewhat surprising” sluggishness of western continental European business in March, the advertising group triggered an almost equally surprising 6 per cent slide in ìts shares. The fall took the stock down to 592½p, just below the level at which they stood, appropriately, at the end of February.