Opec nations earned as much in the first half of this year as they did in the whole of 2007 – thanks both to record oil prices and record production – triggering a big increase in its spending.

Members of the Saudi ­Arabia-led oil exporters’ cartel took home $645bn (£335bn, €430bn) between January and June, just below the record $671bn they earned last year, according to the US department of energy.