According to reports, Taylor Nelson Sofres, Ipsos, GfK and VNU are still in the running. Venture capitalists, among them Cinven, 3i, Permira and Kravis Kohlberg Roberts, are also believed to be interested in buying United's market research business.
Lord Clive Hollick put United's NOP World up for sale in January with a plan to sell it off before he steps down as chief executive in May, when he joins Kravis Kohlberg Roberts. Symbian's David Levin will take up the reins at United.
Although the price belived to have been placed on NOP is £250m, analysts forecast that it could rise as high as £350m.
NOP World includes the market research firms NOP Research Group, Strategic Marketing Corporation, Mediamark Research Inc, Roper/ASW, Market Measures/Cozint and Allison Fisher.
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