UPDATE 1-UK Stocks-Factors to watch on May 31

(Adds company news items, futures) May 31 (Reuters) - Britain's FTSE 100 index is seen opening up 8 points at 7,535 on Wednesday, according to financial bookmakers, with futures up 0.2 percent ahead of the cash market open. * IG GROUP: IG Group Holdings Plc, a British online trading company, said it expected full-year pretax profit and earnings to be "modestly" ahead of last year, with full-year revenue seen rising about 7 percent. * INDIVIOR: British drugmaker Indivior Plc s