UK Stocks-Factors to watch on May 3

May 3 (Reuters) - Britain's FTSE 100 index is seen opening down 21 points on Thursday, according to financial bookmakers. * UNILEVER: Unilever Plc's shareholders approved a new executive pay policy on Wednesday, but the Anglo-Dutch consumer goods group faced a bruising backlash at what is expected to be its last annual general meeting in London. * ABCAM: Biotech firm Abcam said Horizon Discovery had rejected a 270 million pound ($368 million) approach, adding it had gone publi