Minutes after it emerged that the perpetrator of the atrocities in Norway on 22 July was not Muslim but white, blond and Christian, the language of the rolling news broadcasts shifted in tone. This was no longer "global terror": it was a case of "domestic extremism", arising from "local political issues". To think so would be a grave error. The ideology cited by Anders Behring Breivik is one shared by far-right movements across Europe and the US. Breivik, who has described himself as a "nationalist", hates multiculturalism, which he sees as a left-wing plot to weaken European nations, and he hates Muslims in particular.

Breivik's actions were disgusting; yet they also indicated the weakness of the far right in Norway. As we saw in Britain in the early 1980s, after a strong anti-racist movement halted the National Front's electoral progress, fascists and their fellow-travellers are more likely to choose violence when their political ambitions are frustrated. Of greater concern should be those countries where far-right movements have been sufficiently organised to enter mainstream politics. On this list are France, Sweden, the Netherlands and Hungary, among others; and very possibly Britain, too.

The parties' programmes may differ in emphasis - in Hungary, for example, the scapegoats are primarily the Roma - but they have in common a populist rhetoric that draws on mainstream anxieties about a multi-ethnic society, provoked by the economic effects of globalisation. As the free market destroys what remains of social democracy and makes national governments appear to lose control of their own affairs, a surge in nativist feeling is swelling this rising tide of the far right in Europe.

Rather than attempting to bluff their way into power - as Benito Mussolini did with his "March on Rome" - these groups are trying to sink deep roots into communities as they climb the political ladder.

In Hungary, the uniformed Hungarian Guard, a banned group with links to the far-right party Jobbik, wins support by offering "protection" to ethnic Hungarian villagers from their Roma neighbours.

In France, the Front National (FN) has concentrated on regional elections in an effort to capture provincial mairies. Over the past decade, the British National Party (BNP) has attempted a similar project in English towns such as Burnley, Dagenham and Stoke-on-Trent, although it has now been pushed back.

At the same time, we have witnessed mainstream politicians striving to compete on the far right's territory. France's president, Nicolas Sarkozy, has adopted the FN's xenophobic posturing. This year, just weeks after his ruling party, the UMP, scored a mere 2 per cent higher than the FN in local elections, Sarkozy in effect withdrew France from the Schengen Agreement by resurrecting the border with Italy in an effort to stop Tunisian migrants entering the country. Hungary's conservative government introduced a constitution in April that made heavy references to the country's "Christian roots" and laid claim to ethnic Hungarians living in neighbouring states. And in the Netherlands, the Christian Democrats invited the far-right politician Geert Wilders into coalition talks last year.

In the UK, the spectre of the BNP - easily derided as "Nazis", the anti-Semitic and Hitler-worshipping tendencies of some of its leading activists being a matter of public record - has been replaced by that of the anti-Islamic English Defence League (EDL). While this is a street movement, rather than a political party, it has fashioned a widely accepted language in which racism can be expressed. It has adopted some of the trappings of a multi-ethnic society (raising non-white members to positions of prominence; stealing the anti-racist slogan "Black and white unite") and uses religion as a cover for marshalling attacks - both verbal and, increasingly, physical - on a visible ethnic minority.

In July, I attended a seminar at the House of Lords, called by the National Association of Muslim Police to draw attention to the growing threat that the EDL poses. We heard testimony from a young Asian man whose brother had been hospitalised by EDL supporters after the pair happened to walk past a demonstration near their home in Dagenham, east London. We saw video footage of the hatred spewed forth on PA systems at EDL rallies. We even heard how between 30 and 40 EDL demonstrators had turned up at the family home in Lancashire of a Muslim MEP, Sajjad Karim. (Imagine the outcry if an Islamist group had targeted the home of a non-Muslim elected representative in this way.) However, the senior police officers who took part - including Hugh Orde, a contender to become the next Met commissioner - seemed reluctant to accept that the EDL was anything more than a public order problem.

The speed at which the mainstream has accepted the EDL's language is shocking. The Daily Star - a national newspaper with a circulation of nearly a million - has all but endorsed the group, giving it acres of uncritical coverage, culminating in February's front-page story "English Defence League to become political party". (It wasn't true but, judging by the tone of that day's leader column, it is easy to suspect that the Star wished it was.) At least the Star understands that the EDL is a political project. Stephen Lennon, an EDL leader, has been invited on to the BBC's Newsnight twice (most recently on 25 July) and both times has been treated with a sneer in lieu of facing any serious intellectual challenge.

This context should serve as a reminder that we cannot expect the state alone to counter the threat posed by far-right politics effectively. Terrorism by the likes of Breivik may cause untold misery to its victims, but no fascist movement has ever achieved power only by force: even Hitler was invited into government by a ruling class desperate to preserve its position at a time of economic turmoil. We will hear calls to act on "extremism" but it is equally important to consider which elements of extremist ideology parts of the political mainstream share.

This year marks the 75th anniversary of the Battle of Cable Street, in which Oswald Mosley's Blackshirts were prevented from marching through a largely Jewish area of London's East End by grass-roots political action. The EDL plans to march through east London, now home to many British Muslims, on 3 September. We must act to ensure that the fascists of the 21st century, too, are defeated.

Daniel Trilling's book on the British National Party will be published by Verso next year