The commission said yesterday that any merger of WPP and TNS raises competition concerns about market influence in the European television audience measurement services market and in the Irish market research services market.
But it said its concerns were allayed by WPP's promise to sell TNS' market research business in Ireland and to either sell its own stake in its television audience measurement joint venture with AGB Nielsen or the Television Audience Measurement services businesses of TNS.
WPP took out an option in August to sell the TAM business to French market research group for up to £92m.
However, it is still uncertain whether WPP will seal the deal amid opposition from the TNS board, which yesterday after the commission's verdict continued to recommend its shareholders ignored WPP's offer.
At the last count 11% of TNS shareholders had accepted the offer, when a previous deadline for acceptances lapsed on September 12.
WPP extended its deadline to this Friday, September 26, without raising its offer of 175p in cash and 0.1889 of a new WPP share for each TNS share.
TNS shares are currently trading at 252.5p, up 2.3% on yesterday's close, while WPP shares are at 481p, down 1.1%.