UK Stocks-Factors to watch on May 4

May 4 (Reuters) - Britain's FTSE 100 index is seen opening slightly lower on Wednesday, with futures down 0.16 percent ahead of the cash market open. For more on the factors affecting European stocks, please click on * The UK blue chip index closed down 56.30 points, or 0.9 percent, at 6,171.04 points on Tuesday, weighed down by weakness in the mining sector after poor data, with financial stocks also hit by a fall in HSBC following results. * GLENCORE: Mining company Glencore is