Mr Bannon, who fell out with President Trump and has turned his attentions to defending nationalism and opposing migration in Europe, said on a visit to Rome that a rising tide of populism that put the Five Star-League coalition in power would generate a wave of protest votes next May.

“It’s not the end of the EU, but people want their nations back,” he said. He claimed that populist governments in Europe had ended President Macron of France’s dream of closer EU integration. “His project is dead — Italy and Hungary killed it,” he said.

There was further evidence of the populist swell yesterday when Janez Jansa, an ally of the anti-migrant Hungarian prime minister, Viktor Orban, won 25 per cent of the vote in elections in Slovenia.

For Mr Bannon all roads lead to Rome, where he said the alliance of Five Star’s left-wing voters with the League’s hard-right policies offered a lesson for the US. Citing the new Italian government’s mix of “Reaganite” tax cuts and welfare spending, he said: “If we could put Trump’s deplorables together with Bernie Sanders’ economic nationalists, that would be a force which could govern America for many decades . . . Italy is all about nationalists v globalists and they are showing the world the way.”

The former Goldman Sachs banker hesitated over who would pay for the populists’ spending splurge. “I don’t know, but I think they will come up with a very sophisticated plan,” he said.

He also defended the background of the Five Star leader and new deputy prime minister Luigi Di Maio, a former football steward. “It’s like in the American Civil War — Lincoln was a railroad lawyer and Grant was a drunken clerk in his father’s store,” he said. “Look how Virginia Raggi, the Five Star mayor in Rome, used to be a legal secretary.” Critics have argued, however, that it is her lack of experience which has led to potholes and uncollected rubbish.

Yesterday President Trump’s ambassador to Germany, Richard Grenell, provoked outcry by saying he wanted to empower conservatives in Europe to rise up “because of the failed policies of the left”. He said he was “a big fan” of the Austrian chancellor, Sebastian Kurz, who has crossed swords with the German chancellor, Angela Merkel, by rejecting the EU migrant quota system.

The breach of diplomatic neutrality prompted a request for clarification from Germany. Rolf Mützenich of the Social Democrats said: “Clearly the US ambassador sees himself as an extension of a right-wing world movement.”

While in Rome Mr Bannon stayed in his favourite hotel in the capital, the Raphaël, where in 1993 the prime minister Bettino Craxi was pelted with coins by Romans angered by the corruption that would lead to him being convicted. “If they had been around, it would have been the Five Star guys at the front throwing pennies,” Mr Bannon said.

It was not all glowing reviews for the populists over the weekend. In a speech given in Italy, the American financier George Soros suggested that Mr Salvini might be on the payroll of Vladimir Putin and ready to do Moscow’s bidding. Mr Salvini said he had “never taken a rouble”, but added: “Putin is one of the greatest statesmen, while I am ashamed an unscrupulous speculator like Mr Soros was invited to speak in Italy.”

If that sounded like a speech by Mr Orban, who has demonised Mr Soros over his pro-migration stance. Mr Salvini further enamoured himself to the Hungarian leader by pledging on his first day as Italy’s interior minister to bar rescue ships run by charities charity from Italian ports after they pick up migrants. Charities have warned that many migrants will continue to sail from Libya, even if no rescue craft are stationed in the Mediterranean, and more would drown. But Mr Bannon said he believed that the rescuers were a magnet for migrants. “The charities have a moral responsibility for the drownings — it’s on them,” he said.