Steve Bannon has cast himself as a wandering prophet of populism, carting his White House credentials with him as he tours Europe’s nationalist hot-spots – Budapest, Prague, Rome and Paris – over the past five months.

When the former Breitbart chairman continued this messianic march into London’s LBC radio studio during Donald Trump’s visit, it was to defend Stephen Yaxley-Lennon aka Tommy Robinson. A self-declared “enemy of the state” and figurehead of this country’s far right, Robinson is currently serving 13 months in prison for contempt of court. This was due to his decision to film defendants during an ongoing trial on more than one occasion, forbidden under UK law.

But Robinson’s supporters have portrayed his arrest as an attempt to shut him up. On LBC, Bannon called his sentence “outrageous” and depicted it as a free speech issue. “I don’t agree with everything Tommy has to say” but he has “got to be released”, the former Trump strategist told the presenter, the former Ukip leader Nigel Farage.

Bannon’s support of Robinson on a show hosted by a British pro-Trump populist pointed to an important factor in the far right’s recent success: cross-border pollination.

Populism is not new. But its recent incarnation, a potent mixture of nationalism and hostility to globalism, Islam and immigration, has breached borders. This populist movement is mobile: London forums alone have seen speakers from the USA, Canada, Scandinavia, Austria, Croatia and Iran. Charlottesville’s Unite the Right rally had a Swedish presence and was promoted by European social media channels. It was Luton-born Tommy Robinson who helped German protest group, Pegida, establish a UK branch in 2016.

Joe Mulhall, senior researcher at anti-fascist organisation Hope not Hate, says: “The international collaboration is very important as it contributes to the growing sense that the tide is turning on the continent, giving [far right parties] the chance to claim that their movement is able to achieve radical change.”

Identitarianism is a movement with branches across Western Europe and North America, which has been embraced by white nationalists. Austria’s Identitarians launched the Defend Europe campaign – an effort to raise the money to charter a ship and intercept asylum seekers crossing the Mediterranean from Libya – and managed to raise £154,000 in donations. The boat has been supported by groups in Britain including Leave.EU.

The anti-extremist Institute for Strategic Dialogue (ISD) analysed the Austrian Identitarians online campaign strategy. It concluded they were able to reach such a wide audience by using “common grievances such as identity and mass immigration” to unite European and American populists behind their mission.

In the same study, the ISD also looked at online far right activity in the lead up to Germany’s general election last year. Here, too, activists found common ground to unite their audience. But this time their aim was social media domination, not money.

On social channels such as Discord, Reddit and 4Chan, online activists shared tactics on how to launch an international “info-war” that would promote the far right Alternative for Germany (AFD) party, using memes and hashtags. Their efforts were successful. Pro-AFD hashtags were repeatedly featured in Twitter’s top five trending before the election. The AFD eventually came third, making it the first far right party to sit in the Bundestag since World War II.

When the ISD examined the Twitter hashtag #MerkelMussWeg (Merkel must go), it witnessed the importance of that international support. While 62 per cent of the tweets could be traced back to Germany, more than 5.3 per cent were from the UK, 8.7 per cent from Switzerland, 6.8 per cent from the US, and 3.5 per cent from Austria – or 21.3 per cent from these four countries in total.

To reach that international audience, online conversations about how best to promote the AFD took place not only in German, but also in English. This is a tactic that another populist party, the Swedish Democrats, have adopted. Their apocalyptic campaign video for September’s Swedish election – which opens with burning cars, gang rape and terrorist attacks – also features English subtitles. So far, it has been watched over 900,000 times.

Austrian Martin Sellner – leader of the “hipster right” identitarians – has also turned to the English language to broaden his appeal. In 2016, Sellner used his first English YouTube vlog to introduce himself as “an Austrian patriot”. The comments underneath contain declarations of support from the UK, Croatia and Canada, including pleas for more English content.

This cross-border solidarity has migrated from the internet and the streets to the political realm. Last year, Europe’s most successful populist leaders gathered together in the German city of Koblenz. Their meeting had a revolutionary edge, as if a new Europe was in their grasp. France’s National Rally (formerly National Front) leader, Marine Le Pen, declared, “2016 was the year the Anglo-Saxon world woke up!” She was joined by AFD co-leader at the time Frauke Petry, Dutch populist Geert Wilders and Matteo Salvini of Italy's Northern League (LN) which is now part of the country’s coalition government.

Even in politics, populist leaders have created a sense of global community and momentum. To Farage, Le Pen is the “real deal”. Le Pen, meanwhile, called the election success of Austria’s Freedom Party “excellent news”. The Dutch PVV leader, Geert Wilders, has repeatedly called for Downing Street to “Free Tommy!” – most recently via video link at the weekend’s “Free Tommy Robinson” protest.

When he spoke to Tommy Robinson supporters in June, Wilders reinforced that sense of populist global community. “Let me tell you, you will never walk alone,” he said. “At this very moment thousands of people all over the world are demonstrating in front of British embassies.”

Tommy Robinson, someone who broke a basic law of court reporting, has been transformed into a free-speech martyr across the world thanks to Bannon and Wilders. For the wider populist community, Robinson’s case is another excuse to unify a disparate following. “What we are witnessing is European radical right parties using single issues like the Robinson case as a rallying point to build momentum,” says Hope not Hate’s Mulhall.

The irony, of course, is that international co-operation is aiding those who claim to be keenest on erecting walls. In stark contrast, the hard right’s opponents seem paralysed. To effectively fight these cross-border alliances, the liberals and the left need to develop their own.