British Prime Minister Theresa May leaves the Commonwealth Service at...

British Prime Minister Theresa May leaves the Commonwealth Service at Westminster Abbey in London on Monday, March 13, 2017. Credit: AP

As the Westminster terrorist attack was unfolding Wednesday, I looked out at my street and saw schoolchildren walking home to the gentle drone of police helicopters overhead. In the relative calm of the lilac afternoon sunlight, it was as though nothing out of the ordinary was happening; Londoners were asserting their stiff upper lips in the face of chaos unfolding a short distance away.

But the truth is that our celebrated British reserve has been eroding for some time — and we may find it in short supply as further details of the terrorist attack emerge. Americans watching from across the Atlantic would do well to dispense with any romanticized notions of Britons keeping calm and carrying on. British public discourse has become increasingly rabid, xenophobic and isolationist in recent years. And though the deterioration of our discourse certainly did not cause this terrorist attack, it will play a significant role in our national response to it. Brexit has poisoned the well of British political rhetoric, but it is also important to emphasize that the deterioration of our public sphere has been in the making for a long time. And Theresa May and her anti-immigrant cohort must take part of the responsibility.

In 2013, during her tenure as home secretary, May unveiled plans to “create a really hostile environment for illegal migrants,” where banks, landlords and the DVLA (the British version of the Department of Motor Vehicles) would be permitted to check people’s immigration statuses. In recent months, the Home Office has pressured schools, the National Health Service and homeless charities to hand over immigration information about people seeking their services - including children. As home secretary, May was also frequently derogatory about human rights legislation, once recklessly and inaccurately claiming that a man had been granted citizenship on the basis that he had a cat, which allegedly qualified as a “right to family life.” May might talk a good game about inclusivity in the immediate aftermath of a terrorist attack, but her track record suggests a long-term response that will be damaging.

The Brexit campaign itself accelerated the descent of public discourse. A particular nadir was a poster unveiled by far-right politician Nigel Farage just hours before the assassination of the MP Jo Cox by a white supremacist. The poster depicted migrants crossing the Croatia-Slovenia border in 2015, with the only obvious white person in the photograph obscured by a box of text. It read “BREAKING POINT” in giant red letters. One prominent union leader described it as “a blatant attempt to incite racial hatred;” Twitter users have pointed out its similarity to propaganda used by the Nazis.

Home Office figures show that hate crimes in Britain increased by more than 40 percent after Britain voted to leave the E.U. In July 2016, police recorded a 41 percent increase compared to the same month a year earlier. London’s own police force has confirmed it is initiating a plan to increase intelligence gathering and reassure potential victims of racism and xenophobia once Article 50 is triggered, beginning Brexit negotiations.

Just over a month ago, the agenda-setting newspaper the Daily Mail published a fawning article about Geert Wilders, describing him as “the wide boy of European politics” who was seeking a “new patriotic Spring.” Shortly before that, the paper publicly named four judges who had ruled that parliament would have to rule on the government’s plan to leave the E.U., describing them as “enemies of the people” - a phrase used by Joseph Goebbels to describe Jews in the 1940s. The leading proponents of this type of dialogue in Britain have never really spelled out how leaving the E.U. might put an end to migration from majority-Muslim countries — the kind of migration Wilders and others obsessively oppose — but then, that doesn’t seem to really matter.

It is difficult to overstate just how rancid the British political ecosystem has gradually become; how divided the country seems, and how heavily the borders of discourse are policed to root out anyone who doesn’t conform to a certain brand of implicitly white, hyper-nostalgic, empire-worshipping patriotism. It is this context into which we must anticipate the British political response to a terrorist attack. Those who are hoping Britain will conduct itself with trademark stoicism and enlightenment may find themselves confronted with a jingoistic, authoritarian and frankly hysterical nation instead.

This is not to say there is not a sizable portion of Britons who are opposed to the rhetoric of the Daily Mail and its ilk. Indeed, the rise of racist politics has been met with a significant counter-movement, consisting of pro-Europe marches, refugee solidarity demonstrations, and even a vibrant anti-Trump movement which attracted 30,000 people to a protest in central London called with just three days’ notice. London itself is represented by Mayor Sadiq Kahn, a Muslim who has been outspoken about the rights of migrants living in Britain. Just a month ago, Kahn staged a public screening of “The Salesman” by Iranian director Asghar Farhadi as a celebration of the capital’s diversity. He will be a prominent voice in the coming weeks and months, to the relief of many.

But the problem facing progressive Britons in the aftermath of this attack is that, though they may exist in large numbers, they are not controlling the national conversation. The power there lies with expedient politicians and virulently right-wing newspapers, who will attempt to exploit the tragedy to further a xenophobic agenda. The Islamophobic activist Tommy Robinson, former leader of the English Defence League, was giving interviews at the scene before Westminster staff had even been allowed out by police, hysterically declaring that “we are at WAR.” Prominent far-right figure Arron Banks tweeted in the immediate moments following the attack that “illegals” were to blame, and that he felt sick. These are the people who dominate the dialogue of Britain now, and you won’t find a stiff upper lip among them. They will use the events at Westminster to concoct the most frantically un-British response imaginable.

O’Hagan is a freelance journalist based in London writing mainly for the Guardian.