March 7 (Reuters) - Britain's FTSE 100 index is seen opening down 28 points, or 0.5 percent lower on Monday, according to financial bookmakers. For more on the factors affecting European stocks, please click on * The UK blue chip index closed 1.1 percent higher on Friday at 6,199.43, as Britain's mining index climbed to a four-month high, boosted by a rally in the prices of major industrial metals. * GSK: GlaxoSmithKline Plc said its asthma drug, Nucala, which is already approved