The European Commission is demanding more information before it approves UK-based advertising giant WPP's acquisition of US marketing services company Grey Global.

The deal, worth around $1.2 billion (€900m, £640m) was expected to be wrapped up by the end of the year but the delay, needed to satisfy merger rules, will push back the signing of contracts into 2005.

WPP, headed by SirMartin Sorrell, won the auction for Grey Global, against France's Havas and a US private equity firm in September.

The acquisition provides WPP with a roster of blue-chip clients such as Procter & Gamble, Unilever and GlaxoSmithKline and will create a titan large enough to rival the current global leader Omnicom.

Data sourced from Adweek (USA); additional content by WARC staff