Fetch your tin helmets once again. The European Central Bank is opting for a monetary purge. So too is the US Federal Reserve, now ruled from Dallas.

Über-hawks and Cromwellians have gained the upper hand at the great fortress banks. Whether or not they admit it, both are embarked on policies that must lead to retrenchment across the Atlantic world.

The City mood turned wicked as the full import of this policy switch sank in last week. On Wall Street, the Dow's 396-point dive on high volume late Friday had an ugly feel.

"There is now the distinct possibility of a simultaneous sell-off in global bonds, equities and commodities," said Jonathan Wilmot from Credit Suisse.

ECB chief Jean-Claude Trichet has "signalled" a rate rise in July to combat 3.6pc inflation, much to the fury of Paris, Madrid, Rome, Lisbon and Dublin. It is a perilous path for Europe's monetary union.

"I would …