It has been billed as “undoubtedly the most important” European elections since the first polls were held in 1979. 

For the UK, it is all about Brexit. But elsewhere in Europe, traditional political powerhouses face their strongest challenge yet from an array of populist, nationalist and far-right parties.

The looming battle is between those who want Europe to grow more united, and those who favour clawing back power from the EU for their own national governments. 

French president Emmanuel Macron, who has said he wants to avoid Brexit “polluting” the EU after the latest deadline of October 31, has been neck-and-neck in the polls with far-right leader Marine Le Pen.

He is seen as the champion of those who want closer integration, a vision which will face a critical test over the next three days. For Mr Macron, the future of Europe is at stake. 

In an interview with regional newspapers, he said: “I can’t just be a spectator, but must be a player in this European election which is the most important since 1979 — because the EU faces an existential danger.”

The French president has called for a “grand coalition of progressives” to combat “those who want to destroy Europe through nationalism”. 

Meanwhile, Guy Verhofstadt, the European Parliament’s chief Brexit negotiator, has warned the European Union risks being destroyed by a perfect storm of populism, the rise of the far-right, Boris Johnson, Nigel Farage and Russia. 

He told The Times: “What the Boris Johnsons, the Farages, the Le Pens and the others represent is huge. It cannot be business as usual. If European politicians don’t show direction for the future, then we will fall massively back into nationalism, populism, Euroscepticism. 

“If there are not Europeans who can transcend with a vision of a new EU, then if it is not in 2019 it will be in 2024 that they take over the EU and destroy it.”

He added: “There is conspiracy of all the radical right-wing nationalists everywhere apparently with the help of the Kremlin, or of oligarchs round the Kremlin, to disrupt the union.”

Election watchers are expecting significant gains for Europe’s far-right over the course of the weekend.

France’s Ms Le Pen joined populist leaders from 11 EU nations for a rally in Milan at the weekend, as they seek to transform Europe’s political landscape.

She campaigned alongside Italian interior minister Matteo Salvini, who is seen as the key force in the drive for a new populist, far-right alliance across Europe. 

He told supporters: “There are no extremists, racists or fascists in this square. The extremists are those who have governed Europe for 20 years in the names of poverty and precarity.”

He said the “Europe of common sense” had gathered to “free the continent from the illegal occupation orchestrated in Brussels”.

Ms Le Pen promised the Eurosceptics “will perform a historic feat”, insisting they could end up as high as the second-biggest political group in the EU Parliament.

The polls do not back this up. 

Nevertheless, Europe’s populist parties hope to ride a wave of public dissatisfaction and disrupt the political system.

Hungarian Prime Minister Viktor Orban is another key figure. His ruling Fidesz party still belong to the centre-right European People’s Party grouping in the EU, despite being suspended following a row over an anti-immigration poster campaign.

It is thought Mr Orban could co-operate with the new far-right grouping, although he has spoken out against Ms Le Pen.

Divisions among Europe’s populists exist elsewhere, too – including over Russia. 

While Mr Salvini is a well-known admirer of Vladimir Putin, allies from countries such as Denmark and Estonia are openly hostile to Russia.

More than 400 million people are entitled to vote in the European elections, which will determine the bloc’s direction for at least the next five years.

For many, memories of war have vanished. The EU’s role in helping to keep the peace is less of a concern. But taxes, stagnant wages and the gap between the rich and poor are big issues, fuelling recent protests in France. Migration, and how to respond to it, is also front and centre. 

Voter enthusiasm for the European elections has traditionally been muted. Could that be about to change?