The UK government is reportedly planning to sell half its stake in Royal Bank of Scotland, worth £16bn, within two years of a possible first sale in September.Chancellor George Osborne said in June that he wanted the government to start selling its stake in the coming months, with initial sales likely to result in a loss to the taxpayer.If the shares are sold sooner than that, it's likely the government will make an even bigger loss on the initial sale, Reuters said.At 1404 BST, RBS shares were down 2.2% at 351.50p.