The New York Stock Exchange may have to raise its €7.78bn ($9.82bn) bid for Euronext by as much as a sixth to overcome mounting opposition in Europe, according to analysts at JP Morgan. The UK Office of Fair Trading dealt a further blow to a proposed deal as it launched an investigation into whether the tie-up would be anti-competitive.

In a briefing note to investors, Kenneth Worthington and Daniel Harris, two analysts at JP Morgan, said: "Given the increased pressure on Euronext management to consider all options, we believe the NYSE may have to "sweeten" its bid for Euronext to convince Euronext shareholders to accept the combination as well as to preempt a potential bidding war with Deutsche Börse or other [exchange]."