SCIENTISTS from three American universities say that vast plumes of oil are spreading underwater from the blown-out rig in the Gulf of Mexico. BP has denied the claim as it prepares for a new operation to put an end to the worst oil spill in US history — which could see the leak get worse before it gets better.

The company's challenge to several scientific studies is likely to put it further at odds with an increasingly angry Obama administration, which has accused it of playing down the size of the leak in an effort to limit possible fines.

BP's chief executive, Tony Hayward, said it had no evidence of underwater oil clouds. “The oil is on the surface,” he said. “Oil has a specific gravity that's about half that of water. It wants to get to the surface because of the difference in specific gravity.”

Hayward's assertion flies in the face of studies by scientists at universities in Florida, Georgia and Mississippi, among other institutions, who say they have detected huge underwater plumes of oil, including one 120 metres deep about 80km from the destroyed rig.

BP's claim is likely only to further anger environmentalists and the White House, which has grown increasingly suspicious of the company's claims to be frank and transparent on developments. The president's environmental adviser and director of the Office of Energy and Climate Change Policy, Carol Browner, has accused BP of misstating the scale of the leak.

“BP has a vested financial interest in downplaying the size of this,” she said on CBS television. “They will pay penalties at the end of the day, a per-barrel per-day penalty.”

Ed Markey, chairman of the House of Representatives environment committee, has also accused BP of underplaying the scale of the disaster and suggested that it may have a criminal liability.

“The fine that can be imposed upon them is based on how many barrels [pour in to the sea]. It could wind up in billions of dollars of fines,” said Markey. “They had a stake in low-balling the number right from the beginning. They were either lying or they were incompetent.”

In the White House, under increasing criticism for not taking charge of the effort to stop the spill, some officials are saying they have been misled by the company or kept in the dark at key moments.

The Politico website reported that the Obama team was incensed that the company failed to inform it for a day and a half after suspending the failed 'top kill' operation to plug the spill using rubber tyres and mud.

The dispute comes as the company readies its latest effort to contain the flow of oil in to the sea, following the failure of top kill. The new plan involves an intricate operation to cut the top off the damaged riser that brought oil to the surface of the destroyed rig. The intention is to create a flat surface to which to attach a valve that would divert the oil into a pipe and on to a ship.

— The Guardian, London