The gusher in the Gulf of Mexico returned to full force yesterday after BP had to remove a cap that had been containing some of the oil spewing out of its ruptured wellhead.

The coast guard said an underwater robot had accidentally bumped into the "top hat" device and damaged one of the vents. Its failure represents a major setback in efforts to control the spill.

Underwater video showed crude and gas billowing from the ocean floor unchecked for the first time in three weeks yesterday. BP said last night it was trying to reinstall the cap. The beaches of Florida also saw their worst day since the Deepwater Horizon went down 65 days ago, with a thick soup of oil coming ashore in the beach resort town of Pensacola. Fish and wildlife officials reported three beached dolphins washed up on shore.

"It's pretty ugly, there's no question about it," Florida's governor, Charlie Crist, told reporters. The Associated Press said the beach looked as if it had been paved with a six-foot-wide ribbon of asphalt. Only minutes earlier, Ken Salazar, the US interior secretary, had told a congressional committee the top hat device had achieved a new milestone, collecting 27,900 barrels (4.4m litres) of oil in the previous 24 hours – still less than half the oil fouling the Gulf each day.

Salazar also reaffirmed the administration would seek a new, more limited ban on offshore drilling after a judge in New Orleans overturned a six-month pause on Tuesday. The judge, Martin Feldman, was severely criticised by environmental groups yesterday for failing to recuse himself from the case after revealing investment in Transocean, Halliburton, and other firms involved in offshore drilling in financial disclosure forms.

The interior secretary was appearing before the committee to introduce the Obama administration's new head of offshore drilling regulation, Michael Bromwich, and announce a new "zero tolerance" regime for corrupt or lax government safety inspectors.

Thad Allen, the coast guard admiral who is leading the administration's response to the spill, told reporters that workers had detected a possible gas leak in the line that was running warm water into the collection device. The waterline is used to prevent the buildup of hydrate crystals around the collection device.

Initial reports also suggested that the robot may have inadvertently shut down one of the vents on the collection device, raising the pressure within and forcing gas into the warm waterline.

Allen said workers would have to determine whether the device was compromised by the formation of crystals. If so, a new pipe may be needed before they can begin collecting oil again.

The removal of the top hat underlined the enormous challenges of containing America's biggest environmental disaster, just as the Obama administration was hoping to persuade the public it was adopting new safety protocols that would ensure such a spill never happened again.

In his public debut, Bromwich, the new head of a reconfigured agency overseeing the offshore oil and gas industry, told the Senate appropriations subcommittee he was launching an investigative unit to root out corrupt government regulators.

The Bureau of Ocean Energy Management is to replace the Minerals Management Service (MMS), which has been accused of being in the pocket of the oil industry. Bromwich promised a new FBI-style team would conduct internal investigations of the associations between government regulators and industry. "There will be little tolerance for corruption and cosiness," he said. "There will be zero tolerance for whatever was tolerated in the past."

The former prosecutor said his team would encourage whistleblowers and act quickly to root out corruption or complacency among agency officials or the companies they were supposed to regulate.

Even before the Deepwater Horizon rig went down, the MMS was notorious for cocaine-fuelled sex romps between government officials and oil industry executives. In the Gulf, government inspectors were plied with free football tickets or offered jobs by the very same companies they were supposed to monitor.

But Salazar also argued that the MMS had never had the resources it needed to manage Big Oil. He told senators he needs more inspectors to have proper oversight of offshore drilling safety. At present, the agency has 62 inspectors who are supposed to visit 4,000 production wells.

Senators delivered a withering review of its performance. "There was a shameful culture of corruption," said Byron Dorgan, a Democrat from North Dakota.