• Tony Hayward. Picture: Getty
The move by SLI, one of the oil giant's top ten investors, provided some further relief to the company as its shares rose in London and New York after taking a severe battering in recent weeks.
SLI's assurances also came in spite of suggestions by Hayward that the company's second quarter dividend may be suspended to calm political criticism.
In a statement, SLI said: "As a long term investor, SLI has a strong record in taking corporate responsibility seriously and acting in what it firmly believes are the best interests of both the companies our clients invest in and the wider communities in which these companies operate.
"It is our considered view that BP is doing its utmost to deal with the impact of recent tragic events in the Gulf of Mexico and will fulfil its responsibilities.
"We believe that BP has sought to act with complete integrity; consequently we remain fully supportive of Tony Hayward and his management team."
BP shares have taken a huge hit, falling from 655.4p after the rig explosion to below 350p. They ended the week as the FTSE-100's biggest gainer yesterday and, for a second day running, rose in early trade on the New York Stock Exchange, despite new estimates that the oil spill could be worse than previously thought.
Some scientists believe the amount of oil spewing from the blown-out well in the Gulf of Mexico may have been twice as much as previously thought.
BP chairman Carl-Henric Svanberg yesterday visited Downing Street for talks with Chancellor George Osborne and officials.
After the meeting, he said: "I think we have done everything we can to try to fill the well and we have said we would do everything expected from us in cleaning up the beach, taking care of all the claims and learn from this incident and make deep-sea drilling even safer."
He refused to comment on whether BP would pay dividends, what he thought of US president Barack Obama's criticisms or whether Prime Minister David Cameron needed to back the company. Svanberg said he had a constructive telephone conversation with Cameron.
BP's shares recovered from sharp falls earlier in the week as the company came under pressure from the US to halt dividend payments and cover the full cost of the clean-up from the Deepwater Horizon spill.
They dropped 16 per cent on Wednesday and began climbing on Thursday after the oil giant said it could deal with the cost of containing the spill. In London the shares ended the week up 7.2 per cent at 391.9p.
Svanberg has been summoned to meet Obama on Wednesday, and the BP board will meet on Monday to decide whether to suspend or reduce a planned 10 billion dividend.
According to a Downing Street spokesman, Cameron said he was "frustrated and concerned" about the damage caused by the leak, but had made clear his view that BP was an economically important company.
"He said it was in everyone's interests that BP continues to be a financially strong and stable company," the spokesman said.