(Adds futures, company news) LONDON, Aug 6 (Reuters) - Britain's FTSE 100 index is seen opening down by 39-41 points, or 0.6 percent lower on Thursday, according to financial bookmakers. Futures were down 0.5 percent ahead of the cash market open. For more on the factors affecting European stocks, please click on * The UK blue chip index closed up 1 percent at 6,752.41 points on Wednesday, boosted by better than expected results from Legal & General and London Stock Exchange,