UK Stocks-Factors to watch on Sept 21

Britain's FTSE 100 index is seen opening 21 points higher at 7,389 on Friday, according to financial bookmakers. * SHELL: Royal Dutch Shell Plc is in talks to sell its assets in a Gulf of Mexico oilfield to Focus Oil to pay for its takeover of BG Group Plc, Bloomberg reported on Thursday, citing people familiar with matter. * SKY: A protracted $34 billion bidding war for European broadcaster Sky between U.S. rivals Comcast and Twenty-First Century Fox is l