LONDON, Feb 24 (Reuters) - Sunday Times RBS LINES UP 5 BLN POUND SHARE SELLOFF Royal Bank of Scotland is laying plans for a multi-billion-pound share sale that could hand a pre-election windfall to finance minister George Osborne. The taxpayer-backed bank has told its executives to have the business primed and ready to sell shares by the fourth quarter of 2014 - just months before the likely polling day. At least 10 percent of the stock is likely to be sold, repaying about 5 billion pounds ($7.