The pledge cards, initially in English and French versions, will be presented on the eve of the PES Congress at which more than 400 delegates are to adopt the PES election manifesto and elect a successor to PES president Robin Cook.

PES election campaign chiefs plan to translate the pledge cards into all official European Union languages for use during the biggest cross-border election campaign the world has known. The cards will be handed out in shopping centres and markets as well as on doorsteps across Europe.

PES secretary general Antony Beumer said: “The strength of social democracy in Europe, which no other political family can rival, is that we are united around progressive principles and ideas that will improve the quality of life for all our people. We all want to invest in a stronger EU.

“We tackle the tough questions without fear – and we provide clear answers. While we knuckle down to dealing with difficult issues such as migration and social integration, our opponents bluster because they are split from top to bottom over Europe. They offer no coherent vision to voters. How can you pretend to be a European political family if you have federalists and anti-Europeans in your ranks, like the EPP and the Greens

“Our pledge cards will deal with the priorities of the people. They will boil the complexities of European policy down to what matters most. They will spell out why it is of major importance to vote in the June elections to the European Parliament and why a vote for the PES to strengthen the EU is vital.”