Campaigners from Vote 2004 in Britain, Mehr Demokratie in Germany and the Paris-based European think-tank Europe 2020 held a series of events around the summit as part of the European Referendum Campaign.

Hard-hitting adverts on poster vans around the summit site called on Tony Blair, Jacques Chirac and Gerhard Schröder to give their voters a referendum on the new EU Constitution. The adverts call for a referendum in French, German and English.

Campaigners also unveiled a giant advert calling for a referendum at the Brandenburg Gate, near where the leaders were meeting.

Neil O'Brien of Vote 2004 said: "Nine out of ten British voters want a referendum. This new campaign aims to make Europe's leaders listen to the people and give them a vote on Europe's future."

Gerald Häfner of Mehr Demokratie said: "Seven EU members states are holding a referendum on the Constitution. It's time the other Governments followed their example."

Philippe Micaelli of the European think-tank Europe 2020 said: "It looks like an agreement on the EU Constitution is getting close. Now is the time for pro-democracy campaigners across Europe to work together."