Enlargement of the European Union - the inexorable expansion of what was once the six-nation Common Market to today's 25-member community - has always been a mixed blessing.

On the one hand, it has been the most remarkable success story in exporting the stability and prosperity of western Europe to the emerging democracies of eastern and southern Europe. On the other, it has put strains on the old system, and caused a backlash among the voters of countries such as France and the Netherlands, fearful that the coherence and integration of the original EU member states would be diluted by the arrival of a gaggle of newcomers.