The poor man's gold has just made some men poorer. After the Comex exchange raised margins on silver futures - in response to extraordinary volatility and price gains - prices dropped more than 18 per cent in three days. The fall was even harder in speculative vehicles used by retail buyers in search of physical silver, particularly some that traded at a hefty and inexplicable premium to underlying assets.

That premium, along with the violent price decline, should dispel any lingering doubt that silver's recent rise was driven by speculative frenzy. Before Comex acted, silver had risen 57 per cent in 2011, while gold was up 10 per cent. The leading vehicle for US retail speculation, the iShares Silver Trust, has traded the equivalent of nearly 2bn ounces since the beginning of April - close to three times the annual new global supply from mines.