Commission officials, assisted by agents from National Competition Authorities, launched the simultaneous, unannounced searches to look for information about the fee rebates and incentives Euronext is offering for the trading of Dutch securities.

In a statement, The Commission says: "The purpose of the inspections is to ascertain whether there is evidence establishing a breach of European competition rules."

Paris-based Euronext has announced a number of fee cuts this year on Dutch securities amid growing competition in the Dutch market from both Deutsche Börse and the London Stock Exchange.

In September last year, Germany's Deutsche Börse expanded the number of Dutch securities available for trading on its Xetra platform and cut clearing fees by 60% to the same level as German stocks. In February this year, The German exchange reported a tripling in order size and growth in participants trading Dutch equities on the Xetra system.

The LSE launched its EuroSets Dutch Trading service in May this year, which it says undercut Euronext fees by 40%. The LSE claims its Dutch trading service captured two per cent Dutch trade on its first day of operations.

Euronext in turn instigated a wave of fee cuts, slashing up to 30% off the cost of trading in Dutch stocks in April and temporarily waiving certain fees on Dutch securities in May. Euronext said earlier this month it may also cut share trading fees by early next year.

Euronext's plans for further fee cuts coincide with its move to offer cheap trading in UK stocks, which is seen as a response to the LSE's launch of a dealing service in one of its core markets.

Euronext, which put out its own statement regarding the raids, says it is co-operating with the inspection and is entirely confident about its outcome.