Britain’s far right is desperate, angry, cornered, and dangerous, as the Finsbury Park atrocity may well show. In just a year, the number of far-right extremists referred to the government has jumped by nearly a third. Social media abounds with frothing far-right fanatics, screaming about betrayal and vengeance. Both Muslims and the left are firmly in their sights – and we urgently need a strategy to deal with it.

What’s going on? There are all sorts of reasons for this rise. One part is the decision, last year, by the leave camp to run a vicious and dishonest anti-immigration campaign. This campaign had consequences. It’s not just about how xenophobia and anti-immigration rhetoric was apparently conferred with official legitimacy. Radical rightwingers see Brexit as a national revolution – even if this is not the case for most leave voters – an opportunity to wage a culture war against the social values of the left. Theresa May offered a false premise for her vanity general election – that Labour (which voted to trigger article 50) was attempting to subvert the referendum result. “Crush the saboteurs,” screeched the Daily Mail as the election was called. Such rhetoric from the press – like the Mail’s infamous “Enemies of the people” headline – grants legitimacy to the far-right’s worldview, that their opponents are national traitors and saboteurs. So when the attempt to smash the Labour party disastrously rebounded on the Tories, the radical right apparently became terrified that its version of Brexit – which for a small sliver of the population represents a national rightwing revolution – was imperilled. This fuels the traditional far-right “stab in the back” narrative – that traitors have betrayed the nation.

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An ascendant left – coupled with the collapse of Ukip – leaves them feeling cornered, too. Only weeks ago, the likes of ex-Ukip MP Douglas Carswell could crow: “I’m enjoying this election so far. We appear to be witnessing the destruction of the left.” Rather than ending in its eradication, Labour’s left flank is closer to government than at any point in history.

While the far right has always been obsessed with Jewish people, today’s far right is fixated too with Muslims and Islam. After three Islamist terrorist attacks in just a few weeks, some believe that Muslims as a whole are a fifth column, an internal menace to western civilisation. And that’s what leads on to what you could call “Breivikism”. In 2011, the Norwegian fascist terrorist Anders Breivik launched an Islamophobic attack that did not target Muslims. Instead, he targeted young socialists, whom he believed were traitors responsible for mass immigration, multiculturalism and the “Islamisation” of Europe. According to this worldview, the left is the enabler of Islam, and therefore just as culpable for the destruction of the west. It’s the same rationale that led the fascist terrorist Thomas Mair to murder the Labour MP Jo Cox, screaming, “Britain first”.

Hate preachers with a media presence, such as Katie Hopkins and Tommy Robinson, legitimise these fanatics, and fuel further radicalisation. Routine bile against Muslims and immigrants in the British press fuels far-right hatred, too. The danger of the far right will only grow. Britain is now without effective government, led by a prime minister with no authority. The nation is at its most polarised since the war. We’ve gone through the longest squeeze in wages since the 19th century, and wages are falling all over again. The economy may well tank. Brexit negotiations will lurch from crisis to crisis, fuelling far-right paranoia that Britain is under attack by external enemies and internal traitors.

Online, those on the far right bubble with growing rage against Muslims and the left, demanding action against both. Perhaps they’re all just keyboard warriors, dribbling with rage in stained boxer shorts. Perhaps. But they are like cornered rats, and we know how cornered rats behave. If any good comes from the evils of the Finsbury Park atrocity, it is a renewed determination to confront the far right.