France on Sunday night dealt a potentially fatal blow to the European Union's constitutional treaty as voters resoundingly rejected it in a referendum.

The 56 per cent victory for the No campaign sparked an immediate political firestorm in France and could stall Europe's 50-year integration drive. The French vote could also have a knock-on effect in the Netherlands, which is due to hold its own referendum on Wednesday. The latest opinion polls show Dutch voters are also likely to vote No.