Among other things, BP's 75-page brief submitted last week to the 5th US Circuit Court of Appeals asked the court to overturn US District Judge Patrick Barbier's November decision rejecting the oil giant's arguments, contending that Patrick Jurneau had secretly drafted court papers filed against BP before he was appointed claims administrator.

"BP presented the District Court with extensive, recently uncovered evidence that Mr Juneau actively advocated against BP's interests and litigated against BP in this very case as part of his work for the state of Louisiana in 2010 and 2011," BP spokesman Geoff Morrell said in a statement last week.

"That work is a clear and serious conflict of interest - one that Mr Juneau failed to disclose properly and that disqualifies him from serving as Claims Administrator."

BP said it had identified hundreds of millions of dollars in payments that should never have been paid to claimants and accused Juneau of turning a blind eye to fraud in the settlement program. An independent auditor recently noted that nearly 20% of certain claims were paid even though required documentation for those losses was absent.

Critics have long maintained that Juneau allowed a culture of corruption to persist through lax internal policies, the Louisiana Record said, adding that at least five senior level executives in Juneau's operation had been fired or resigned after being accused of engaging in questionable ethical behaviour.

Barbier ruled that Jurneau, before his appointment, told BP and at least six of its attorneys that he had been a state consultant for the spill and that the oil major had missed the boat, filing its motion to remove Juneau too late.

However, BP said it didn't realise the extent of Juneau's state work until late July, when lawyers found his 2010 contract among tens of millions of pages of documents.

"Mr Juneau's gross mismanagement of the settlement program - which has resulted in poor performance, ethical violations among the program's leadership and wasteful administrative costs that have risen to more than $US40 million per month - is well documented and separately warrants his removal," Morrell said.

Earlier this month the US Supreme Court declined to review the multi-billion dollar Deepwater Horizon settlement agreement designed to compensate victims of the Deepwater Horizon incident.

The refusal to review the case leaves in place a lower court's ruling that claimants do not have to prove they were damaged by the oil spill to receive a settlement. BP and others have argued this ruling runs counter to existing case law.

Morrell said at the time that BP would continue to agitate for fairness in the settlement.

"We nevertheless remain concerned that the program has made awards to claimants that suffered no injury from the spill - and that the lawyers for these claimants have unjustly profited as a result,'' he said.

"On behalf of all our stakeholders, we will therefore continue to advocate for the investigation of suspicious or implausible claims and to fight fraud where it is uncovered."

BP's latest filing said claims centre expenses for this month were expected to be over $40 million, with the total for this year estimated at $463 million.

However, lead plaintiffs' attorneys Steve Herman and Jim Roy said in a joint statement that a claims centre audit demanded by BP contradicts the company's allegations of poor performance.

"Now that it has lost its Supreme Court bid to get out of the settlement, BP's latest attack on the Claims Administrator is simply a desperate attempt to disrupt the payments by any means necessary," Herman and Roy wrote.