The traditional third option favoured by the EU in recent years – muddling through and "kicking the can" – is looking increasingly difficult to sustain.

The question now confronting Europe – and the voters in Britain’s own referendum – is whether all these stresses now being placed on the European Union will force a genuine re-ordering along more “common sense” lines or, sooner or later, lead to the collapse of the project altogether.

“The EU at the moment is like one of those cartoon characters that went hairing off a cliff ... At some point everyone will realise there is nothing but thin air, and then whole thing will plummet down to earth.”

There are those, like Charles Grant, the director of the pro-EU Centre for European Reform, who look at the Europe Union today and find that – despite all its undoubted problems - the most remarkable thing is that “everywhere, it appears that the centre appears to be holding”.

Despite all the fears stirred by the anti-austerity protesters and nationalist up-start parties like AfD, when it comes to the crunch, he argues, the moderate majority still holds sway. So when Ms Le Pen threatened to win real power after the first round of last December’s regional elections, the centre-ground parties closed ranks to defeat her - just as they had done in 2002 when her father, Jean-Marie, reached the second round of the presidential election.

Similarly in Germany, the AfD is surging in the polls, but that country’s history and the in-built majority of Angela Merkel’s coalition means that while the AfD might win seats in the Bundestag, they will never sit in government in modern Germany.

Economically things are also looking up – the Eurozone has begun to reform itself, putting in stronger fiscal controls and better banking supervision which should help it withstand the next downturn, whenever that comes. And though the ECB’s stimulus programme may have been late in coming, it has now has kick-started growth.

On this view, the impact of the politics of protest is also over-stated. Even the once-radical Syriza, which threatened to tear up the European rule book, has been forced to institute reforms that will unlock the debt relief that should, at least, stabilize the Eurozone’s ugly duckling.

Spain has also been growing well this year – despite not having a government – and Portugal, while talking tough on ending austerity, has submitted a budget thatafter some judicious fudging was acceptable to the European Commission.

But to other analysts, these are cold comforts when set against the massive challenges that Europe faces – and the apparent lack of political will needed to solve them.

Finding solutions to Europe’s major problems – controlling immigration, fixing the single currency, ending economic stagnation and tamping down rising nationalism – require European-wide co-operation at a time when national politics is heading in precisely the opposition direction.

The AfD may not get in to government in Germany, but already its influence can be felt, sapping the ability of a Mrs Merkel - already weakened by her handling of the migrant crisis - to sell any form of European economic comprise to the German electorate. In France Ms Le Pen may never be president, but the threat of her rising popularity prevents Francois Hollande from agreeing to the visa-free travel for Turkish businessmen and tourists that will be necessary to keep the EU-Turkey deal alive.

In Britain, Ukip ostensibly failed at the last general election, winning only a single seat at Westminster, but that is a poor measure of its influence: Ukip won more than 12 per cent of the vote (three times the number of votes as the Scottish National Party, which won 56 seats) and was instrumental in forcing a referendum on Britain’s EU membership that may change the direction of the entire continent.

And while it is true that the Eurozone is growing again thanks to easy ECB money,the threat of deflation still looms large and the fights with Germany makes clear that the deeper structural issue of how to run a currency union without a political union remains further than ever from being addressed.

For Professor Bickerton, Europe might have gone over the edge already without us realizing it. “The EU at the moment is like one of those cartoon characters that went hairing off a cliff and is now running wildly in thin air,” he says. “At some point everyone will realise there is nothing but thin air, and then whole thing will plummet down to earth.”

Whether Europe manages to regain its footing is an open question, but as the Austrian presidential election demonstrated, the establishment and centrist forces are now under everywhere under sustained pressure, and there is more to come. In the Netherlands, the Islamaphobic party of Geert Wilders is currently topping the polls, with parliamentary elections due in March; France will hold a presidential election in April and May 2017 that – win or lose - will give Marine Le Pen a massive popular platform; as will Germany’s presidential election the far-Right AfD. In early 2018 Austria’s far-Right Freedom Party will get another serious bite at power in 2018 parliamentary elections.

But first, the most pressing test comes on June 23: the impact a Brexit – still possible on the back of a low turnout - could be momentous indeed.

Additional reporting: Henry Samuel in Paris, Justin Huggler in Berlin, Richard Orange in Malmo, Matthew Day in Warsaw, Senay Boztas in Amersterdam, Nick Squires in Rome, James Badcock in Madrid, Matthew Holehouse in Brussels

Editors: Jessica Winch

Graphics: Mark Oliver