BP was at the centre of fresh takeover speculation after weekend reports suggested the Obama administration has told ExxonMobil – the world's largest oil firm – that it would not stand in the way of a takeover bid for the stricken British rival.

Before the Gulf of Mexico oil spill BP was Britain's biggest company with a stock market value of £121bn. Since then more than £50bn has been wiped off its share value and a number of potential bidders are rumoured to be circling to take advantage of its weakened state.

Oil industry sources were quoted as saying that ExxonMobil had been given a green light by the US government to "take a look" at BP. A merger would create a group with a stock market value of $400bn (£265bn). Both firms refused to comment on the speculation.