Tony Blair has refused to confirm whether September's planned increase in petrol tax will go ahead, despite prices at the pumps rising to their highest levels for four years.

The prime minister told MPs yesterday that the soaring costs of oil were not due to the government but to high world demand and low stocks.

Yesterday the chancellor said he would be urging major oil exporting countries to increase production in an attempt to halt price rises.

"We will be consulting with Opec [the Organisation of Petroleum Exporting Countries] on the recent rise in oil prices, and urging them to raise oil production to meet world demand at the prices that they themselves have said are sustainable," Gordon Brown said.

Later, Ed Balls, the chief economic adviser to the Treasury, told the Foreign Press Association in London: "Oil now presents a real and emerging risk to the global economy."