Barack Obama and John McCain on Monday stepped up their increasingly tetchy exchange over high petrol prices, with Mr Obama accusing his rival of being in the “pocket of big oil” and Mr McCain accusing his opponent of hypocrisy.

Mr Obama, whose opinion poll numbers have slid sharply since his trip to Europe and the Middle East last month, on Monday unveiled a “comprehensive energy plan” that promised to wean the US off foreign oil while providing short-term relief to consumers.