Socialists make up coalition governments in a further four countries. According to European Parliament figures, two out of three voters across the Union have voted for a socialist party in the latest elections held in each of the member states.
Political analysts in Brussels cannot recall a period in the history of the EU when socialist parties have gained such support. For the first time, if the left-leaning governments band together, they can wield a qualified majority in votes within Europe's Council of Ministers.
Only two countries, Germany and Spain, are still run by centre-right governments. However, experts were swift to caution against claims that socialism is on the march. The evidence from recent European elections suggests that voters have been motivated by anger with the incumbents rather than love for their left-leaning challengers.
"The fact is that it is very hard to be popular in government at the moment," says Peter Ludlow, director of the Centre for Policy Studies in Brussels.
Commentators point out that high unemployment and welfare cuts are top of the electorates' concerns but are beyond the power of any one government to solve.
"The fact that governments are changing across Europe so quickly is evidence of a massive conspiracy by Europe's political elite, who fight elections on the pretence that if they change policies they can influence these events which are beyond their control," says Stanley Crossick, head of the Belmont research institute.
When Europe's socialist leaders meet in the Swedish city of Malmo this week, they are certain to discover that when it comes to the details of policy on jobs and welfare, their differences remain wide. Mr Blair, for example, will want to keep his distance from the French socialist drive for welfare and a shorter working week, preferring to emphasise his more centrist vision of flexible labour markets.
LEFT IN POWER
The Socialists and Social Democrats
IN POWER ALONE: Sweden
Portugal Greece Italy Britain
RUNNING A COALITION:
Netherlands Denmark Austria
PART OF A COALITION: Ireland Luxembourg Belgium
IN OPPOSITION: Germany