The far right is organized and growing. These Nazi salutations are serious.

Last week in London were about 15,000 supporters of Tommy Robinson, former leader of the English defense League. Some were aggressive, attacked the police and physically threatened anti-racists who were peacefully protesting against them.

Among their number were people raising their arms in Nazi salutes. This is a serious situation that demands attention from everyone who wants to combat the racist politics that have regrettably emerged in many parts of Europe. In the European parliament, I have seen an increase in the number of MEPs who are openly hostile to migrants, Muslims and multiculturalism. We do not want British politics to be infected by the same developments.

Robinson has a long record of far-right activity, criminality and violence. His real name is Stephen Yaxley-Lennon and he adopted his pseudonym when he founded the EDL in 2009, partly to hide his past as a former member of the fascist British National party.

He makes no distinction between Muslims as a whole and those of that faith who may have acted violently. “I’d personally send every adult male Muslim that has come into the EU over the past 12 months back tomorrow if I could. Fake refugees,” he tweeted in early 2016.

Robinson’s supporters are drawing strength from the growth of an international movement of racists in Europe and the contemptible attitudes of Donald Trump. This was clear on Saturday, when not only did the Dutch far-right leader Geert Wilders speak, but also there were messages of support from Louis Aliot, vice-president of France’s National Rally (previously named National Front); Filip Dewinter, a leading member of the Vlaams Belang party in Belgium and a well-known apologist for Nazi collaborators during the second world war; and Steve Bannon, a former adviser to Trump.

Make no mistake, this is an attempt to build an “alt-right”, pro-Trump movement in Britain. Saturday’s demo included chants of “Make Britain Great Again”. The event was organised by Raheem Kassam, former editor-in-chief of Breitbart, and ex-EDL deputy leader Kevin Carroll, and backed by Bannon with forces to the right of the Conservative party in Britain from Ukip, ex-BNP and National Front supporters and football firms around the Football Lads Alliance (FLA).

Such links make it obvious that Robinson is not a free speech champion. He was jailed after pleading guilty to committing contempt of court. Far from extending freedom, last Saturday’s rally will encourage more outrages such as the Leeds Mosque and Gurdwara (Sikh Temple) arson attacks. It could inspire a repeat of assaults such as the one in June in Bolton that left a woman in a critical condition.

The present movement in support of Robinson is building on the activities of the FLA. Launched last year, it said it aimed to unite “the football family against extremism” and “bring about a change in anti-terrorist legislation”. But whatever the motivation of some of its participants, its real agenda soon became clear. On its march of tens of thousands in central London last October, Robinson was treated like a celebrity by many marchers. The official line of the FLA was that it did not welcome Robinson, but the reality was already becoming apparent.

Just look at the FLA’s secret Facebook group. The page, monitored by FLA administrators, includes posts by members calling for London’s mayor, Sadiq Khan, to be “hanged” and for Diane Abbott to be “run over”. There are also posts claiming Finsbury Park mosque attacker Darren Osborne is a scapegoat and suggesting he was right to plot to kill the Labour leader, Jeremy Corbyn.

Tensions inside the FLA – partly about the proceeds from merchandise sales – led to a split. The Democratic FLA can now mobilise more people than the original FLA. It is clearly well funded.

We are at a crucial moment and cannot allow such forces to grow. Trump’s racism, his “Muslim ban” and plans for an anti-migrant wall have encouraged the racist right everywhere, and will be a major reason why he will face mass protests against his visit to Britain.

I fully support the Together Against Trump demonstration coinciding with his visit on 13 July and Stand up to Racism’s call for a peaceful protest on 14 July against another pro-Robinson demo. Everyone who cares about the future of our society should come together for the politics of unity, not division.