The announcement followed Hayward's return to the oil business last week, when his investment vehicle Vallares
The enlarged group will likely be big enough to enter the FTSE 100 index of blue-chip London-listed companies.
A spokesman for BP, responding to a report in the Sunday Telegraph, said it had been aware for some time that Hayward may be considering his future on the board of TNK-BP. The spokesman said were Hayward to leave the board of the joint venture, he would be replaced by another BP-nominated director.
In an interview with the Sunday Telegraph, Hayward said he did not have any plans to step down from either TNK-BP
The paper said Hayward did not believe he would have the time to devote to TNK-BP.
Hayward quit as BP chief executive after its blown-out Macondo well caused the worst ever offshore oil spill in the United States. As part of the crisis, Hayward was vilified by much of the American press for a string of comments, including when he said he wanted to get his life back.
The news comes as Britain's prime minister, David Cameron, travels to Russia for a visit focused on business and trade. Cameron will travel with more than 20 business executives, including BP chief executive Bob Dudley.
BP has been engaged in a spat with its partners in TNK-BP, who have alleged billions of losses due to BP's failed plan to establish a parallel joint venture with state-controlled Rosneft.
Last week, black-clad special forces raided BP's Moscow offices and searched for documents related to the failed Rosneft deal.
(Reporting by Kate Holton; Editing by Dan Lalor)