What turned the tone of British politics from civil to bitter?

The admonition was authoritative and stark. “Intimidation in public life presents a threat to the very nature of representative democracy in the U.K.”

But that warning two years ago from the Committee on Standards in Public Life, an independent body advising then-Prime Minister Theresa May, fell on deaf ears. Bullying, insults, and threats have become commonplace in British political life since. And as the current election campaign in the United Kingdom moves into top gear, many politicians fear that things could get even worse.

Some of them can’t face that prospect.

“Nobody in any job should have to put up with threats, aggressive emails, being shouted at in the street, sworn at on social media, nor have to install panic alarms at home,” Heidi Allen, a former Conservative member of Parliament, wrote to her constituents explaining why she is not running for reelection next month.

The “nastiness and intimidation” of public life had “exhausted” her, she wrote.

So toxic has the political atmosphere grown – fouled largely by angry disagreement over Brexit, which has split the country in two – that a quixotic group of prominent political figures last month launched an award for civility in politics “celebrating politicians who behave with courtesy and decency to one another.”

“Politics have gone from occasional belligerence to a default mode of aggression,” worries Stewart Wood, a Labour member of the House of Lords behind the £3,000 ($3,800) prize. “It’s like the Wild West; there aren’t any rules anymore about how you engage in politics.”

The prize “won’t change the world,” he says, “but we want to shine a spotlight on people who make a difference.”

A lost temperateness

British politics have never attracted the faint of heart. Winston Churchill once left the House of Commons with blood streaming down his face after an opposition member had thrown the parliamentary rulebook at him, and Norman Tebbitt, one of Margaret Thatcher’s ministers, thought his career got a boost when a Labour leader called him a “semi-housetrained polecat.”

Nor is fury a stranger to Britain’s streets: The yearlong miners’ strike against pit closures in 1984-85 expressed the genuine rage felt in many communities. But when Jo Cox, a Labour MP campaigning to stay in the European Union, was murdered just before the Brexit referendum in 2016, her assassination was the first of a sitting MP since 1812 that was unrelated to Irish nationalism.

Some see the new fractious and intolerant tone of political argument – in Parliament, on the streets, and online – as somehow “un-British”: out of step with a supposed tradition of fair play and polite pragmatism. When the London-based think tank British Future carried out a values survey in 2013, the most important characteristic of “being British” was found to be “respect for people’s right to free speech, even if you don’t agree with them.”

“People would like to have that self-image of temperateness back,” says Sunder Katwala, who runs British Future. “There’s a hankering after things we share that bring us together.”

Nonetheless, “the country is polarized at the moment, and defiance of publicly accepted norms of expression is at a peak,” says Annemarie Walter, a political analyst at Nottingham University. At the same time, she adds, “the British public seems more accepting of certain types of behavior than they were in the past.”

“I’m not a snowflake,” says Lord Wood. “I don’t want to take the passion out of politics. Heated exchanges are good, and massive disagreement is absolutely crucial” in a democracy. But “the line has been blurred between political differences and personal attacks,” he says. “I want to redraw it, and the award is a device to draw attention to this.”

The taint of Brexit

A powerful catalyst for the changes that have swept through British political life is the debate over whether and how Britain should leave the European Union – a debate still unresolved 3 1/2 years after voters in a referendum chose narrowly in favor of Brexit.

Brexit, which is a major theme of the current election campaign, has become much more than a question of trade relationships and has come to involve citizens’ sense of identity. “People cleave to their position on Brexit more strongly than to their political party choice,” says Anand Menon, an expert on U.K.-EU relations at King’s College London.

“It has become fundamental to how we define ourselves, and just like the culture wars in the United States, people are genuinely angry,” Professor Menon adds.

And they are expressing that anger in increasingly aggressive – sometimes illegal – fashion. Notably Anna Soubry, a former Conservative MP who supports remaining in the EU, was subjected to a lengthy torrent of abuse as she was being interviewed on live TV outside Parliament. A nearby protester repeatedly called her a “Nazi” and a “traitor”; he was later given a suspended prison sentence.

Earlier, Ms. Soubry had received death threats on Twitter and over the phone calling for her to be “Jo Coxed,” a reference to the murdered Labour MP.

Many MPs, especially women, have suffered such abuse, which is often sexist, racist, or obscene on social media. During the last general election campaign in 2017, senior Labour politician Diane Abbott, who is black, received almost half of the abusive tweets sent to female MPs, a report by Amnesty International found.

Ms. Abbott told Amnesty’s researchers that she received hundreds of racist letters a day, some illustrated with swastikas and pictures of monkeys. “It’s the volume of it which makes it so debilitating, so corrosive, and so upsetting,” she said. “And the sheer level of hatred that people are showing.”

Some women MPs complained in Parliament that the warlike language pro-Brexit Prime Minister Boris Johnson was using to attack opponents, such as “surrender” and “betrayal,” risked triggering more threats against them and perhaps real violence. His dismissal of such fears as “humbug” caused uproar.

Unsocial media

Fueling and facilitating the trend to incivility and worse is social media.

Alison Goldsworthy, a former campaigner for the Liberal Democrats who now heads the Depolarization Project at Stanford University, first noticed that during the Scottish referendum on independence from the United Kingdom in 2014.

“We engage most strongly with things we feel strongest about,” she points out, “so campaigners were encouraged to take more and more hard-line positions to get that engagement. Facebook recommends that campaigners be provocative. So there is a race to the bottom.”

And when campaigners succeed in stoking emotions, their supporters can express those emotions as rudely and as extremely as they like with a few anonymous and unaccountable clicks of the keyboard.

Mr. Katwala, of British Future, cautions against mistaking online arguments for real-life opinions. “At the school gate or in the pub, where people chat, they are quite civil,” he says. “Online you only see the other side’s hyperpartisans.”

When British Future organized a national conversation about immigration last year, it asked participants to say on a scale of 1 to 10 whether immigration had had a positive or negative impact on the U.K. Most people who answered a pollster's questions and those in panels were somewhere in the middle. When asked the same question in an open online survey, a majority of respondents chose either the minimum or maximum score.

The highly polarized atmosphere online distorts reality, Mr. Katwala points out, “but a lot of our politics is being driven by thinking that online polarization is how everyone thinks.”

Political polarization

At the same time, there is little doubt that political tensions in Britain are particularly fierce because the two main political parties have been taken over by their more extreme members.

Most of the Conservative Party’s 160,000 members are older white men, of whom a majority would rather see the U.K. pull out of the EU with no deal than any other scenario, even if that did significant damage to the economy, two polls earlier this year found.

In the Labour Party, the Momentum faction – strongly supportive of leader Jeremy Corbyn’s unashamedly socialist platform – has attracted hundreds of thousands of new party members who have radicalized Labour’s grassroots.

With them, complain Jewish Labour Party activists and MPs, came a wave of anti-Semitic online comments and talk at party events that went well beyond sympathy for the Palestinian cause to taint political discourse with a particularly insidious brand of incivility.

“I used to get a bit of abuse 10 years ago when I spoke about Israel,” says Dame Louise Ellman, who represented a Liverpool constituency in Parliament for 22 years. “But it became much worse later,” she says, after membership in her constituency Labour Party increased fivefold upon Mr. Corbyn’s election as party leader, “which brought some very unpleasant views.”

Dame Louise resigned from the Labour Party last month, complaining that “Jewish members have been bullied, abused, and driven out” of a party in which “anti-Semites have felt comfortable and vile conspiracy theories have been propagated.” She is not standing in the coming election.

Earlier this year another prominent Jewish MP, Luciana Berger, left the Labour Party arguing that anti-Semitism there was an expression of “a tribal conviction that anyone with a different view or perspective is a deadly enemy.

“Whereas it once existed only on the fringes of left or right, it now surfaces in the mainstream, and is given the soapbox and megaphone of social media,” Ms. Berger wrote in the Observer weekly. “It is pure poison.”

Looking for moderation

Societal leaders have weighed in on behalf of civility in political life. The archbishop of Canterbury, head of the Anglican church, recently warned Mr. Johnson against “inflammatory” language, saying that “in a time of deep uncertainty, a much smaller amount of petrol is a much more dangerous thing than it was in a time when people were secure.”

And Queen Elizabeth, in her traditional Christmas message to the nation last year, said that “even with the most deeply held differences, treating the other person with respect and as a fellow human being is always a good first step towards greater understanding.”

Whether their injunctions will weigh more heavily than the Committee on Standards in Public Life is open to doubt. “The election campaign will make politics more emotional, more intense,” says Dame Louise. “I suspect that personal threats and abuse won’t go away very easily.”

Some observers suggest that an eventual resolution of the Brexit question, one way or another, would clear the path to a more consensual and civil way of doing politics. “There is a strong sentiment that if we can get over this, we can start to put things together” again, says Mr. Katwala.

Others are dubious. “Political entrepreneurs have seen what you can do when you mobilize identity” in the way Brexit campaigners on both sides have done, says Professor Menon. “There will always be people out there willing to make use of that.”

Nor does he see any immediate signs that either of the two major parties will move back to the moderate center, which might have presaged a reversal of the current tendency to incivility.

Mr. Katwala believes that fewer opportunities to vote might have a calming influence. By the end of this year, the electorate will have been through three general elections, two European elections, and two referendums since 2014; that has kept the political temperature high.

Instead, Mr. Katwala would like to see more of the sort of national conversation that British Future fostered around immigration last year in 60 cities and towns. Panels of citizens sitting down around a table to talk things over face to face, which means they are concerned to be polite, “hold inherently civilizing debates,” he says.

What chance for reform?

It would help, suggests political scientist Annemarie Walter, if Britain had an electoral system that resulted more often in coalition governments, as in Germany or the Netherlands, which “inherently have mechanisms to limit incivility.”

“When politicians have to work together after elections, that discourages negative campaigning,” Dr. Walter says. “If they are too hostile, or overstep social norms, others may refuse to work with them.”

But neither of the large British parties has any interest in abandoning the “first past the post” system that minimizes smaller parties’ chances of success, and they seem unlikely to introduce any reforms to that system.

Rather, says Ms. Goldsworthy, who from her perch at the Depolarization Project is also helping to organize the “civility in politics” award, “it takes some kind of a shock to the system to get people to change. I think we are approaching the time when that will be the only way to turn things around.”

Whether it comes from a shock or less violent cause, “ultimately it will have to be a cultural change” in British political life “that makes people find it unacceptable to behave like that,” says Lord Wood. And it is up to politicians to lead the way. “It has to come from a determination among MPs to show restraint.”

Otherwise, he says, “when Brexit eventually dies down, I fear we will find that the aggressive way of doing politics will have become the norm.”