THE recovery of the world's biggest advertising agency, WPP, continues apace with half year earnings climbing by 40 per cent. Taxable earnings in the first half raced ahead to £443 million sterling from £28.6 million in the first six months of 1995. The interim dividend is up to 0.556p from 0.445p on earnings per share 2p higher at 5.8p. Its debt reduction programme is continuing as planned with borrowings at the end of June standing at £169 million, compared with £217 million a year earlier. Three years ago, WPP's borrowings stood at £372 million.