Turnover in Turquoise's Block Discovery platform, which is aimed at large investors moving big blocks of shares, hit more than 600 million euros ($664.02 million), exceeding volumes seen in June.

Dark pools are popular with institutional investors trading in big amounts as they limit the market impact of a large order in the market.

Large trades around merger and acquisition activity, in particular Japan's Softbank agreeing to buy ARM Holdings (>> ARM Holdings plc) as well as the ongoing deal between AB Inbev (>> Anheuser-Busch Interbrew) and SABMiller (>> SABMiller plc), also helped boost volumes, the firm told Reuters.

"In cases of high volatility, e.g M&A or Brexit, the service has demonstrated that it offers block liquidity for investors wanting to move very large orders quickly and without moving the market," said Robert Barnes, the chief executive of Turquoise.

Overall, Turquoise had a 17 percent share of dark pool trading in Europe in July, making it the third largest venue behind BATS Europe and UBS' multi-lateral trading facility, according to Thomson Reuters Market Share Reporter.

(Reporting by Atul Prakash, Editing by Vikram Subhedar)