BP has failed to update its oil spill emergency plan in the Gulf of Mexico more than three months after the Deepwater Horizon rig exploded in apparent violation of federal regulations, the Observer has learned.

The company was lambasted by US politicians for having a response plan which, even before the explosion, appeared to have serious flaws. Errors included a proposal highlighting the need to protect sea walruses, even though none exist in the Gulf, and listing one wildlife expert who died four years before the plan was approved.

BP has admitted it has still not revised the plan. Yet according to the federal agency responsible for offshore drilling, the Minerals Management Service (MMS, now renamed BOEM), operators must submit a revised plan within 15 days if "a change occurs which significantly reduces your response capabilities" and if "a significant change occurs in the worst case discharge scenario".

Both these conditions apply to BP, according to one Texas law firm. Mikal Watts of Watts Guerra Craft said: "After a catastrophe like Deepwater Horizon, MMS regulations require that BP submit a revised oil response plan. BP hasn't, and the Gulf of Mexico continues to be at risk because of BP's failure to follow the law."

Politicians also said that the disaster had exposed the plan's worst-case discharge scenario as inaccurate. Under BP's plan, the worst case envisaged was a spill of 250,000 barrels a day 30 miles off the shore of Louisiana. Even though the size of the Deepwater Horizon spill was much smaller, BP was still unable to prevent the oil from hitting the coast.

A BP spokesman denied the company needed to file a revised plan, saying: "An incident does not trigger automatic re-submittal of an oil spill response plan… Once we have gathered the learnings from the Deepwater Horizon incident, we will update our plan and submit it."

Asked about the BOEM regulation to revise the plan within 15 days in changed circumstances, the spokesman said, "we believe we are in compliance with the regulation". BOEM said it was still reviewing BP's original plan, and that the company had not submitted a revised version.

Congressional hearings into the oil disaster have heard that MMS routinely failed to enforce its own laws in the Gulf. President Obama has promised to tighten up the regime.