BP’S board has unanimously agreed to sell the oil giant’s 50pc stake in TNK-BP to Rosneft for cash and shares worth as much as $28bn (£17.4bn).

The deal, brokered by the chief executive, Bob Dudley, will end years of wrangling with BP’s partners in the Russian joint venture, and redefine BP’s Russian strategy. Investors, though, have expressed concerns over corporate governance issues.

The Sunday Telegraph understands that BP will receive between $10bn-$14bn cash plus a 15-20pc stake in Rosneft, the Russian energy conglomerate, valued at $10.9bn to $14.6bn based on its $73.3bn market valuation.

The negotiations were thought to be moving towards a higher number of shares in Rosneft than cash, to give BP a greater say in the Russian business’s future strategy.

While the final details of the agreement were still being finalised this weekend, formal confirmation of the deal could come as early as tomorrow.

Sources said key negotiation points yet to be resolved include how many seats BP will be given on Rosneft’s board. It is thought two seats may be possible but one is more likely.

In addition, BP was attempting to extract an indemnity from Rosneft protecting it from legal action from Alfa Access Renova (AAR), the oligarch-backed entity which owns the other half of TNK-BP. BP executives are said to be concerned about the likelihood of legal action from AAR, which scuppered BP’s last attempted share-swap agreement with Rosneft 18 months ago.

BP’s board, chaired by Carl-Henric Svanberg, voted to approve the transaction on Friday night.

A source close to the discussions indicated that as long as the executive team managed to deliver a deal within the conditions, the board will not need to vote again on the matter.

Another delay could come from the need to seek regulatory approvals from the relevant Russian authorities for the share allocation, as well as drawing up the complex set of agreements that will bind the two companies.

Rosneft holds about 12.5pc of its own shares in reserve and it is thought the remaining shares will be allocated from Rosneftegaz, the investment vehicle that owns Russia’s shares in the company.

The Russian company is being advised by Bank of America Merrill Lynch on the transaction, and it is thought the cash payment will be financed by a syndicated loan.

BP will become Rosneft’s second largest investor as a result of the deal, adding the new shares to the 1.25pc stake it has owned in the Russian company since its 2006 float.

One BP source indicated that given Rosneft has taken control of the oil sector in Russia, partnering with it reflects a long-term commitment to the former Soviet country from BP. A second source indicated that a separate deal which will see Rosneft purchase AAR’s 50pc of TNK-BP could be completed as early as Thursday.

There are growing investor fears that BP’s decision to sell its TNK stake to Rosneft may create corporate governance risks. Five of BP’s top 20 investors expressed concerns about the deal to The Sunday Telegraph. “Having shares in Rosneft is a long way from ideal,” said one top 10 shareholder, adding that it left them feeling “deeply uncomfortable”.

“Exactly what is corporate governance in the context of Russia and Rosneft? And what assurances has BP sought?” asked another investor.

Investors said that without a clear dividend policy from Rosneft, owning such a valuable asset would prove worthless to shareholders: “We want BP to dispose of this [TNK] stake – but this is a whole new problem.” In an interview with this newspaper in February, Mr Dudley said he would consider share buy-backs in the future.

BP declined to comment.