LONDON (Reuters) – WPP, the world’s biggest advertising group, said it would merge its two largest communications agencies Hill & Knowlton and BCW, in the latest internal tie-up aimed at driving efficiencies within the company. London-based WPP, which owns creative agencies such as Ogilvy and media planner GroupM, said on Thursday that the combined group would be renamed Burson and have 6,000 staff in 43 markets, adding that there were synergies between the units. WPP is battling to eke out growth after tech clients reined in spending on marketing last year and amid tough conditions in China. …