Harris Associates, a Chicago-based investor, has emerged as the biggest shareholder in Euronext after the pan-European exchange briefly opened its shareholder register. Threadneedle Investments, a UK fund manager owned by American Express, has also revealed that it has sharply increased its stake in the London Stock Exchange. This now stands at more than 10%, making Threadneedle the LSE's biggest shareholder.

Under French law, the details of Euronext's shareholders are not public information, but for three weeks after it announced its potential interest in bidding for the LSE, institutional investors were required under UK takeover rules to disclose their holdings.