John Napier, the chairman of insurer RSA, has written to Mr Obama urging him to stop his relentless criticism of BP following the Gulf of Mexico oil spill.

US anger has contributed to a 45pc drop in the company’s share price since the accident on April 20, which killed 11 men and triggered a disastrous leak. The US authorities may issue an injunction to stop BP paying a dividend, and analysts fear it could be barred from government contracts or even have its assets seized.

Florida’s Attorney General, Bill McCollum, yesterday demanded that BP put at least $2.5bn (£1.7bn) into a holding escrow account in order to ensure money is available to cover potential damage and claims in his state alone.

Amid rumours that BP was looking at bankruptcy protection for its US unit, the company’s share price dropped 26.05, or 7pc, to 365.5p. Raymond Dempsey, BP’s vice-president of strategy, told a Senate ­hearing that there was “no such suggestion, indication or concern” about receivership.

BP is understood to be preparing to take a tougher line against US politicians, sending Carl-Henric Svanberg, its chairman, to take on a more active role behind the scenes in America. Mr Obama has requested a meeting with Mr Svanberg on Wednesday, the President’s first meeting with BP officials since the accident happened in April.

Tony Hayward, chief executive, will return to the UK next week, after being lambasted by Mr Obama over tactless comments about the spill.

Shareholders, analysts and business leaders rallied around BP last night, as the National Association of Pension Funds estimated that around £12bn of British pension money is invested in the oil firm.

George Luckraft, manager of a £1.7bn fund for Axa, said Mr Obama’s threats were “ridiculous”, adding that he should not be interfering with a private company’s dividend. “We’re holding our BP stake and are going to sweat it out,” he said.

Fred Lucas, an analyst at JP Morgan, said: “We would like the British government to raise a diplomatic red flag regarding the sanctity of UK incorporated entities. Such political interference is an issue that has profound implications for all industries, not just the oil industry.”

Prime Minister David Cameron last night appeared to back the US reaction to the spill ahead of a phone call to Mr Obama, saying he “understood” the feelings towards BP. A US official emphasised that relations between the two countries would not be harmed, stressing it was a matter between America and a private company.

As part of Mr Svanberg’s tactics to improve relations with the US, the BP board will ­consider an unprecedented deferment of the dividend.

BP has managed to cap almost all the oil coming from its leak, but heavier concentrations of tar yesterday washed up on Florida beaches. Scientists said up to 50,000 barrels of oil a day may have been leaking, twice the previous estimate.