The Party of European Socialists has launched Europe's first cross-border election pledge card.

The party congress, involving more than 400 delegates, was also expected to adopt the PES manifesto for the European parliament elections in June and elect a successor to president Robin Cook.

The PES was expected to unveil four key commitments to the electorate in Europe’s first-ever election pledge card.

Campaign chiefs plan to translate the pledge cards into all official EU languages for use during the biggest cross-border election campaign in history following EU expansion.

The cards will be handed out in shopping centres and markets as well as on doorsteps across Europe.

PES secretary general Antony Beumer hit out at his political rivals.

"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," he said.

"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."