UK Stocks-Factors to watch on May 8

May 8 (Reuters) - Britain's FTSE 100 index is seen opening 13 points higher at 7,580 on Tuesday, according to financial bookmakers. * VIRGIN MONEY: Virgin Money said on Monday it had received an all-stock takeover offer from rival CYBG Plc, a proposal that values the British lender at about 1.6 billion pounds ($2.17 billion). * TAKEDA-SHIRE: Takeda Pharmaceutical is nearing an agreement to buy rival drugmaker Shire Plc, a deal which could be announced on Tuesday, the deadline s