The front-runner continues to be Euronext — the Paris-based operator of four continental exchanges and Liffe, the London futures exchange.

The second bidder, the Deutsche Börse, dropped out of the auction in March and is not expected to re-enter the fray, even if its earlier approach is cleared by the commission.

The provisional ruling, which will initiate a round of negotiations with any bidders still interested in buying the LSE, was expected earlier this month.

The delay, which the commission said reflected the complexity of the case and the “huge amount of evidence”, is seen as increasing the likelihood that any bidder will be saddled with conditions governing how the London market can operate under its control.

The main concern would be any regulation of tariffs that can be charged.

London users have expressed concern that prices could rise to reflect the costs of the bid.

In December the Börse indicated that it was prepared to offer 530p a share, valuing the LSE at £1.3 billion.

Euronext came in with an expressed interest early this year. The two parties spent several months negotiating with Clara Furse, the LSE chief executive, before the Office of Fair Trading (OFT) referred the bids to the commission at the end of March.

The OFT said that the two potential bids gave rise to concerns about competition, in spite of efforts by the two to give “constructive undertakings” over their future behaviour. Those could include price controls to prevent it exploiting its dominant position if it took control of the LSE.

The commission then said that it was concerned over the lessening of competition between European exchanges if the LSE were taken over, and whether this would result in lower fees for customers from the resulting cost savings.

One market observer commented at the weekend: “It’s not the sort of shoo-in we were expecting.”

The LSE share price has been remarkably resilient despite the uncertainty. It closed on Friday at 504¾p, within striking distance of the initial German offer.

A number of analysts believe that even if the current bid period ends in stalemate, the pressure on world exchanges to consolidate would mean an eventual bid from elsewhere.

This could come from the New York Stock Exchange, itself now going through a merger with Archipelago, an electronic share-trading firm.

Some London users have suggested that the LSE should, under foreign ownership, be operated as a utility, a body whose fees to customers would merely cover operating costs and necessary investment, rather than as a profit centre.

If the commission moves towards this view, this is likely to be unacceptable to Jean-François Théodore, Euronext’s chief executive.

On Friday Numis Securities, the broker, reiterated its view that the LSE would eventually be taken over at a price in the region of 555p.

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