LONDON, Oct 5 (Reuters) - A pipe for feeding stock and bond transaction prices to investors across the European Union would improve the bloc’s capital market, a study for stock exchanges by consultants Oliver Wyman said on Tuesday. The EU’s executive European Commission has said it may have to mandate the creation of a ‘consolidated tape’ (CT) of market transaction prices to improve transparency on what’s happening across 600 stock and bond trading venues in the bloc. The study for the Federation of European Securities Exchanges (FESE) said a tape for transaction prices for stocks, bonds and exchange-traded-funds with a 15-minute delay would provide the best benefit from the 50 million euros ($58.08 million) it would cost. Other options looked at were price quotes, near real-time prices, or end of day prices and volumes. A tape, long a feature of the U.S. and Canadian stock market, has been a longstanding aim in Europe, made more urgent as the EU seeks to deepen its capital market after Britain, Europe’s biggest financial centre, left the bloc last December. “For a CT to be useful, it must provide a complete overview of market activity to investors,” FESE Director General Rainer Riess said in a statement. The report said a CT should be administrated by an independent body such as the EU’s securities watchdog ESMA, powered by specialized technology and advised by users and contributors. FESE said the persistence of “low quality” market data and the “damaging extent of dark” trading away from traditional exchanges is also a barrier to full transparency. ESMA has said that 50% of share trading is off-exchange, but banks dispute this figure. The Commission has pledged to examine what it called a "dog"s dinner" of market data here before making changes to markets. Once a CT has been set up and its benefits proven, Oliver Wyman said there could be incremental decreases in the delay time towards a more real-time service. ($1 = 0.8610 euros) (Reporting by Huw Jones; Editing by Andrew Heavens)