“The spectre of a break-up is haunting Europe and a vision of a federation doesn't seem to me like the best answer. We need to understand the necessity of the historical moment,” he said.

Mr Tusk’s blunt words come amid a raging battle this week within the EU’s socialist and conservative blocs over how to respond if Britain votes to leave the EU on June 23.

There are mounting signs that the Dutch, Scandinavians, and many Eastern European states may not be willing to back any push by Brussels for a ‘Plan B’ of deeper political union – with an ‘EU army’, and joint foreign, security, and border policies - once the British are out of the way.

Nor does the rhetoric from Germany, France, and Italy match reality in any case. The eurozone’s failure to back monetary union with a badly-needed fiscal union a full six years into the EMU debt crisis has nothing to do with Britain, which has eagerly encouraged such a move. It is chiefly due to a German and Dutch veto.

“There would undoubtedly be a Franco-German declaration the day after Brexit, but the truth is that the differences between France and Germany over the way forward for the eurozone have never been greater,” said Charles Grant from the Centre for European Reform.