BP's attempt to draw a line under its troubles in the US by axing its chief executive has been blunted after Tony Hayward said he would be "too busy" to attend a Senate hearing on Thursday.

The oil company risked further inflaming a delicate trans-Atlantic relationship when its directors described BP as a "model of corporate social responsibility" despite being at the centre of the worst oil spill in American history.

Speaking to journalists at the company's London headquarters, Hayward claimed that he had been unfairly "demonised and vilified" in the US, where Barack Obama and other politicians have been severely critical of BP's actions and taken exception to some of Hayward's public comments.

The Senate foreign relations committee has asked Hayward to appear in Washington to explain BP's alleged role in influencing the release of the Lockerbie bomber in order to win drilling rights in Libya.

But Hayward said today he could not go because "I have got a busy week [in the office]". BP said it would send another representative to testify at the hearing.

This infuriated committee member Robert Menendez who made reference to the BP boss's pay-off – a year's salary and his pension pot, together worth £11m. "It is apparently more important to BP and Mr Hayward to focus on his multimillion dollar golden parachute than to help answer serious questions about whether the company advocated trading blood for oil," he said.

The committee later postponed the hearing after Menendez accused those asked to attend – two Scottish officials, former justice secretary Jack Straw, Hayward and a second BP official – of stonewalling. "It is utterly disappointing … that none of these key witnesses will co-operate with our request to answer questions before the Senate foreign relations committee. They have stonewalled," Menendez said.

Hayward, explaining his departure from the group he has led for three-and-a-half years, had argued that the Gulf of Mexico blowout on 20 April had left BP a different company. "I believe for it to move on in the United States it needs new leadership and it is for that reason I have stood down as the CEO. I think BP's response to this tragedy has been a model of good social corporate responsibility. It has mounted an unprecedented [spill] response."

The same message was given by Bob Dudley, the BP director in charge of the Gulf clean-up, who will take over the top job from Hayward in October.

Dudley, who will become BP's first American boss, described the company's reaction to the blowout on the Deepwater Horizon as an "unprecedented corporate response" adding that very few companies could have done what it did.

And the future chief executive said the accident was "very complex", caused by multiple failures of equipment and triggered by "a number of companies".

Asked whether Hayward had been unfairly treated, Dudley praised Hayward's leadership, adding: "I think that time will show whether that has been fair or not." He later said he expected his colleague's reputation to be restored, but declined to say whether Hayward could eventually get a wider role in addition to the one he will be nominated for as a non-executive director at the company's Russian joint venture, TNK-BP.

Hayward hinted that he felt he had received an inappropriate level of abuse. "Whether it is fair or unfair is not the point. I became the public face and was demonised and vilified. BP cannot move on in the US with me as its leader," he said, adding that like many aspects of everyday existence "life isn't fair ... sometimes you step off the pavement and get hit by a bus".

Hayward accepted some of the gaffes he had made, such as wanting to "get his life back", had damaged the oil company.

"It may not have been a great PR success. You can argue about whether it could ever have been a great PR success, operationally we capped the well and cleaned up a hell of a lot of the oil."

Hayward was contrite when asked if he could have done anything differently. "Was I close to perfect? Absolutely not. Did I make some mistakes? Of course I did. With the benefit of hindsight would I have done anything different? Of course."

The man who took over from Lord Browne in 2007 defended his right to receive his £10m retirement benefits as well as a year's contractual salary of £1m after spending all his working life at BP. Hayward said: "I have not got some special deal. I am just walking away with a pension that I earned over 30 years."

BP's Swedish chairman, Carl-Henric Svanberg has also come under pressure to quit. A major shareholder is reportedly calling for him to take responsibility for the disaster by resigning, but Svanberg said the board had not asked him to stand down and he had no intention of leaving.

The Swede also denied that a decision to sell $30bn (£19bn) of assets to raise cash to pay for the Gulf clean-up, and liabilities now estimated at the same price, would turn BP into a second tier company.