WPP, the FTSE 100 communications agency, is to buy a majority stake in impactasia, an independent public relations agency with an established network of offices in Greater China.Clients of impactasia already include Rolls Royce, Guinness and the Mandarin Oriental Hotel Group.impactasia's unaudited revenues to the end 2010 were approximately HKD 23.5 million/ (£1.94m), with gross assets at the same date of approximately HKD 12.8 million (£1.06m).The exact price paid for the controlling interest was not disclosed.Greater China is already WPP's fourth largest market and the firm employs 13,000 people across the region.BS