As recently as last July, when RBS was struggling to shore up its balance sheet, executives insisted the bank would not sell its BoC stake. They argued the shareholding in China's second-largest bank was part of RBS's long-term approach to building a presence in the region.

Indeed, Sir Fred Goodwin, the former chief executive, decided he would rather put RBS's UK insurance operations up for sale than cash in on the BoC investment, which he had personally negotiated in 2005, shortly before the Chinese bank listed on the stock market.

RBS was one of several foreign financial institutions that eagerly snapped up small stakes in the three largest Chinese banks ahead of their stock market listings in 2005 and 2006, spotting the one-off chance to gain access to China's domestic banking market.