The British oil company's US president, Robert Malone, and its head of Alaskan operations, Steve Marshall, ate humble pie in an appearance before members of Congress's energy and commerce committee. "We have fallen short of the high standards we hold for ourselves," Mr Malone said. "BP America's recent operating failures are unacceptable."

They were accused of ignoring warning signs and cutting back on maintenance checks in the run-up to discovery of corrosion and a spill that forced the shutdown of half of the Prudhoe Bay oilfield in August.

Mr Marshall said: "These spills occurred on my watch. As president, I'm in charge of the overall business in Alaska and the buck stops with me."

Their admission of blame did little to pacify congressmen, who said their constituents were paying higher prices at petrol pumps as a result of BP's shutdown. The Prudhoe Bay field accounts for 8% of US domestic oil production.

BP was accused by the committee of having safety policies "as rusty as its pipelines". In a packed hearing room, the committee demanded to know why it had been 14 years since BP last subjected its 29-year-old eastern pipeline to inspection by "pig" - a maintenance robot. Another pipeline operator, Alyeska, testified that it sent pigs along its lines every two weeks.

Edward Markey, a Democrat, told the BP executives: "You were essentially driving a car with over 100,000 miles on the clock without bothering to spend the money and time on maintaining it."

Another Democrat, Jan Schakowsky, said: "If this company had spent as much on inspection and maintenance as it does on advertising and lobbying for lower taxes, none of us would need to be here today."

BP's corrosion manager in Alaska, Richard Woollam, refused to answer questions, pleading the fifth amendment on advice from his lawyers. He was allowed to leave.

Mr Marshall repeatedly declined to discuss details of maintenance, saying that he was "not a corrosion expert" and did not have information available. He did agree with suggestions that BP had avoided using pigs because of a build-up of solids within the pipe which could have been dislodged, causing damage to pumps and further erosion.

Staff from the congressional committee recently visited Alaska to gather evidence. They said employees expressed fear of intimidation and harassment if they spoke out. A Democrat member, Bart Stupak, said staff turnover and a poor working culture in BP's corrosion control unit had created a "chilling atmosphere" for employees reporting problems.

BP responded last week by appointing a former district judge, Stanley Sporkin, as an independent ombudsman, and providing a 24-hour phone line for whistleblowers.

It emerged yesterday that the US justice department has subpoenaed an entire stretch of pipe as evidence in a criminal case being drawn up against BP. The US department of transportation is also investigating the company's conduct.