UK Stocks-Factors to watch on Sept. 15

Sept 15 (Reuters) - Britain's FTSE 100 index is seen opening down 13 to 15 points, or 0.2 percent lower, on Thursday, according to financial bookmakers. * The UK blue chip index closed 0.12 percent higher at 6,673.31 points on Wednesday, breaking a three-day losing run, as firmer mining stocks enabled the market to recover some ground. * BP: BP does not plan to increase annual investments this decade but still expects to bring nine new projects online in 2017 as it focuses on impro