For many years, the commodities sector was an economic backwater. No longer. The proposed flotation of Glencore, valuing the company at up to $73bn, is a sign of how capital is flooding back into the sector. But the excitement generated by soaring commodity prices is tempered by concern. A prolonged surge in demand for raw materials has fuelled fears about commodity-driven inflation.

Glencore added another worry this week, when it revealed its share in a number of raw materials markets. Its dominance is far greater than thought – and that is bad news for competition.

In 2010, the trader controlled 60 per cent of the third-party market for zinc and half the market for zinc concentrates and copper; for lead, the figure was 45 per cent and for alumina, 38. True, the third-party market is only a small part of the overall market for commodities – most trades are done directly between industrial consumers and producers. But such a concentration of resources in the hands of one organisation still matters because the spot prices the third-party market sets are used as a reference in other transactions.