WPP must bid for TNS by July 9 or go away

LONDON (Reuters) - Martin Sorrell's WPP Group Plc (WPP.L) must launch a formal bid for British market research group Taylor Nelson Sofres Plc TNS.L by July 9 or walk away, Britain's Takeover Panel said on Wednesday.

TNS has opened its books to WPP but would prefer a merger with German group GfK Holding AG (GFKG.DE).

TNS has so far rejected two proposals from WPP, the world's second-largest advertising and marketing group, as undervaluing the firm and its chairman, Donald Brydon, welcomed the "put up or shut up" ruling from the panel.

"WPP has had a substantial period of time to consider whether or not it intends to make a proposal that properly reflects the value of TNS ... shareholders deserve an end to this extensive period of uncertainty," he said in a statement.

The planned merger of TNS and GfK would create the world's second-biggest market research company, after AC Nielsen, worth around $4 billion.

WPP said it was continuing to monitor the situation.

TNS and GfK shareholders are due to meet on July 18 and July 21 respectively.

(Reporting by Ben Hirschler; Editing by Quentin Bryar and David Holmes)