France, the Netherlands, Austria, Finland and Hungary could all follow Britain out of the European Union in a rash of anti-Brussels rebellions, according to a paper prepared by the German finance ministry.

The warning came in a document obtained by German media as foreign ministers from the six EU founding member states met in Berlin to discuss how to shore up the ailing European project.

It came as Emmanuel Macron, the French economy minister, joined calls for EU reform, urging a new road map for the bloc to be put to a pan-European referendum.

"We've never had the courage to organise a true European referendum in its real sense. This next project must give it that strength," he told a conference. "We would first build this new project with European peoples and then submit this new road map, this new project, to a referendum," he said, adding that the idea was to have one single referendum across the bloc.