(Corrects first bullet to say index closed down 0.4 percent at 6,828.54 points) Aug 23 (Reuters) - Britain's FTSE 100 index is seen opening up 24 to 28 points, or 0.4 percent, on Tuesday, according to financial bookmakers. * The UK blue chip index closed down 0.4 percent at 6,828.54 points on Monday, with commodity-related stocks leading the market lower following a drop in metals and crude oil prices. * RANK GROUP: Casi** operator Rank Group Plc said on Tuesday Britain's de