Royal Bank of Scotland Group is to sell its aviation unit to Sumitomo Mitsui Financial Group of Japan for $7.3 billion (£4.7bn), the bank confirmed last night.

The deal, which will be announced to the stock market today, marks the end of a fierce auction that saw Sumitomo Mitsui pitted against China Development Bank Corporation in the final stages.

Sumitomo Mitsui fended off competing offers from the Chinese bank and US banking group Wells Fargo to buy the business from RBS, which is 82%-owned by the UK Government.

It is believed that Sumitomo Mitsui became the leading bidder after concern grew that state-owned China Development Bank would struggle to gain Government approval for a purchase in a timely manner.

At $7.3bn, the disposal will be Royal Bank's biggest since it received a £45.5bn Government bail-out during the 2008-09 financial crisis, the biggest bank rescue in the world. Royal said last night that it expected the sale would be completed before the end of the third quarter.

Royal Bank's aviation business is one of the biggest plane lessors after General Electric's Gecas and AIG's International Lease Finance Corporation.

Earlier, shares in Royal Bank nudged up 1.33% after reports that it was in talks about selling its mergers and acquisitions (M&A) arm in the Middle East.

The stock finished up 0.32p at 24.42p as details on plans to overhaul its investment bank began to emerge.

Simon Penney, RBS chief executive for Middle East and Africa, told Reuters that the M&A business was being sold.

The division, which has offices in Abu Dhabi and Dubai, had been working on four M&A deals in the region, including The Coca-Cola Company taking a 50% stake in Saudi Arabia based drinks business Aujan Industries for £639m.

Mr Penney added: "It is a global decision to exit cash equities and M&A. We had some pretty good mandates live and we'll see all deals closing. We will honour all client obligations but we won't be originating any new business."

Reuters suggested a sale could be done in the next few months, with up to five parties having expressed an interest.

The decision to offload its M&A arm is part of RBS's plans to cut thousands of jobs from its investment bank and knock £120bn off its balance sheet in the next three years. Around 3500 jobs are at risk around the world in the global markets division.

Lazard has been appointed to find buyers with Commonwealth Bank of Australia, Bank of China, ANZ, DBS Bank, Mizuho Financial, Oriel Securities and Royal Bank of Canada all understood to have expressed interest in parts of the RBS empire.

Senior staff are also looking into the potential for management buy-outs at certain parts of the business. Other reports suggested Royal may want to wrap up sales of the businesses ahead of interim results in February but the bank would not comment on the speculation.

The restructured investment bank will focus on fixed income, foreign exchange, debt financing, transaction services and risk management.

Chief executive Stephen Hester has sold or wound down more than £160bn of assets since taking over from Fred Goodwin.