James Henderson, CEO of Bell Pottinger, has quit ahead of expected sanctions imposed by Britain's ethics watchdog for its controversial work in South Africa.

James HendersonJames Henderson

"Whilst I had no involvement in the account, there were warning signs that I should have heeded. Therefore I must take responsibility," he told the BBC.

Henderson, who with fiancee owns about 40 percent of the firm, promised to keep a close watch on his investment.

BP is considering strategic alternatives, which may include a sale or buyout.