Jan 18 (Reuters) - Britain's FTSE 100 index is seen opening up 8 points on Thursday, according to financial bookmakers. * BHP: Global miner BHP on Thursday reported a 3 percent rise in second-quarter iron ore production year over year and said it expects to meet its full-year target as prices for the steelmaking ingredient outperform forecasts. * WHITBREAD: Activist investor Sachem Head has asked Whitbread to consider a break up of its Costa Coffee chain from its hotels and rest