LONDON — This city feels like the capital of a country that has been hijacked by a tribe for whom London represents everything that they hate: they hate its prosperity, its cosmopolitanism, its social diversity, its cultural exoticism, its bawdiness and most of all its un-Englishness.

The hijackers are the Little Englanders, a noisome and virulent strain of nativism that has taken power in Westminster. For several generations they had been successfully marginalized. Now they are mainstream, put there by the vote to leave the European Union, Brexit. They dominate the ruling Conservative party and came to power, narrowly, as unexpected winners, gloating.

But the nation has suddenly woken up to a calamity. The Brexiters had no plan for how to proceed. The new government is clueless.

Indeed, Brexit is proving to be the greatest single destruction of economic value ever carried out deliberately as an act of policy by a British government.

In the last two weeks the pound sterling has hit a 60-year low against the dollar (a dive greater than that of the Argentine peso) and economists are warning that by the end of 2017 it could sink to a one-to-one parity with the dollar.

But never mind the metrics, they are bad enough but something more sinister is under way. By far the most decisive issue driving the Brexit campaign was immigration. Anti-immigrant sentiment was first stirred by Nigel Farage, the oleaginous leader of the United Kingdom Independence Party, UKIP (currently a smarmy camp follower of the Trump campaign). UKIP released the toxin but it soon spread far beyond their constituency and was fueled by opportunist Brexit campaigners on the far right of the Conservative party.

And here we get to the evil banality of the whole movement. The Brexiters are fundamentally delusional. The delusion is a form of patriotism based not on the traditional flag-waving of great power conquests, but on a pureness of nationhood that in order to be preserved must withdraw from all external influences and engagements.

This retreat into a demented xenophobia sits oddly with its opposite: the centuries-long conviction that the world needed to be civilized by the only force enlightened enough to deliver it: English imperialism.

And, in a performance that would be entertaining were it not so consequential, these contradictory versions of English exceptionalism are displayed in one man, the man who more than any other politician was responsible for the Brexit campaign’s narrow win in the July referendum: Boris Johnson.

But then contradiction has never bothered Johnson. As a two-term mayor of London he rode the London economic rollercoaster. On his watch and helped by his gift for boosterism the capital city became a model of outward-looking commercial engagement, the equal of New York as an engine of unfettered capitalism and exceeding New York in its embrace of globalization—the very same globalization that Brexiters blamed for a flood of immigrants that they believed was taking their jobs and contaminating their island culture.

Mayor Johnson became simply “Boris”—a beguilingly nimble player on the national stage, instantly recognized by his thatch of unruly blond hair that was seized upon by cartoonists as visual shorthand — He grew happily into the role of glib clown, always ready be a prop in publicity stunts.

But people who had dealings with Johnson as mayor have told me that beneath the mask of clown there was always a man of ruthless ambition. He was never interested in detail. His management style was hands-off to the point of negligence. And his end game was clear: become prime minister.

He wrote a biography of Churchill and affected Churchillian gestures—forward-looming brow and a fondness for aphorisms.

After leaving the mayor’s office Johnson’s ambition was pretty clear to David Cameron, the prime minister and leader of the Conservative party. Cameron and his circle disliked Johnson and did their best to keep him in a box. But Johnson saw a path to power through the party’s lunatic fringe, a restless right wing of Little Englanders who had always hated Europe.

Apostasy followed. Johnson the champion of the big world view shamelessly became Johnson the rebel and most potent voice of the Brexit movement.

Party insiders believe that Johnson never expected Brexit to prevail. After boldly leading the charge and having a noble defeat he would be established as a party leader in waiting—waiting for Cameron to stumble. Instead, Cameron’s campaign to keep Britain in the European Union failed.

But Johnson was still denied the prize. He was too discredited by his switch to Brexit.

The party instead chose Theresa May. She had not supported Brexit but her support for Cameron had been muted. And one of her first and most inexplicable acts was to appoint Johnson as foreign secretary, a choice that at best was seen as a cynical move to keep the support of the Little Englanders and at worst as a serious error of judgment. The idea of Johnson having your back induces paranoia, not comfort.

Since then an extraordinary thing has happened. It seems that all along there have been two Johnsons living under the same blond mop. There is Johnson the loyal servant of Little England and then there is Johnson the lover of England’s global hegemony. He told his party’s annual conference, to great applause:

“When I go into the Map Room of Palmerston I cannot help remembering that this country over the last two centuries has directed the invasion or conquest of 178 countries.”

The Map Room is in the Foreign Office, today as much a museum of empire as a working office. Lord Palmerston was both foreign secretary and twice prime minister when he directed the final conquests of empire in the Victorian era—he can be imagined strutting the Map Room and pointing a finger at the next piece of the earth that required an imposed dose of civilization.

It may be that Johnson’s apparent schizophrenia does actually embody the real tragedy underlying the Little Englander mentality. They dream of the power that subjugated the peoples of 178 countries but they also accept that it can now only ever be a dream. Simultaneously they accept the diminishment of their country’s world role. It is a price worth paying if it preserves the values they believe to be uniquely English—the values that enabled and underpinned the glory of empire.

Of course, this meets a classic definition of madness—to be able to hold both views and still see them as a reasonable basis of political belief.

It did not take long to see where this kind of madness would take Theresa May.

The London School of Economics is much more than its name implies. For generations it has been an incubator of progressive political and social ideas as well as educating 34 future heads of state and 18 Nobel laureates. Some of its graduates even went on to lead revolutionary movements that ended British rule in the colonies. It was, and is, a symbol of British academic open-mindedness.

Imagine, then, the outrage when May’s government announced that the group of experts who would be advising officials in Johnson’s Foreign Office on the technical details of negotiating British exit from Europe would be purged of anyone who did not have a British passport—even though LSE academics who were not British citizens had already been recruited.

Showing remarkable restraint, the LSE protested: “We believe academics, including non-UK nationals, have hugely valuable expertise, which will be vital in this time of uncertainty around the UK’s relationship with Europe and the rest of the world.”

The appearance of discrimination on the basis of nationality—with all its echoes of Nazi Germany in the 1930s—was reinforced when Amber Rudd, who took over the Home Office (a combination of the equivalents of the Department of the Interior and Homeland Security) from Theresa May, said that more positions in British universities and businesses should be reserved for those of British birth. (About 15 percent of the research and teaching staff at British universities are from Europe.)

Rudd even said that companies should have to hand over lists of their foreign workers to the government. There are 3 million citizens of European Union countries working in Britain who now feel under threat of deportation once the process of Brexit is complete.

It got worse. The next target was the institution that the country values above all others, the National Health Service. Ministers suggested that Britain should produce more home-grown nurses, doctors and specialists to replace those recruited from abroad. (The NHS would cease to function without its large contingent of staff at all levels who are foreigners.)

These official steps seem to be pandering to an anti-foreigner prejudice that gets expressed in more openly violent ways. Newly released statistics from the Home Office show an alarming 19 percent jump in hate crimes. Half of all hate crimes recorded by the police are race-based and there has been a 34 percent jump in crimes ascribed to religious prejudice.

British Muslim women are reporting frequent vocal abuse if they wear head scarves. But another large immigrant community has found itself targeted for violent attacks—Poles. A stereotypical “Polish plumber” has become a lightning rod for people who say they are losing their jobs to Eastern European immigrants prepared to work for lower pay.

The surge of bigotry in the streets has been evident for some time. What is new is the way it has been made almost respectable by the recent actions of the government. A powerful editorial The Observer newspaper spelt it out. The paper said that ideas are emanating from senior ministers that are “as alarming as they are unpleasant. They carry a gross whiff of xenophobia. They convey an inescapable undertone of racism and intolerance. They are a return to the narrow, delusional world of Little England.”

It’s always a sign that a British government is in trouble when the country’s resourceful headline writers start to play with a minister’s name to describe their incompetence. Even some pro-Brexit factions thought that Rudd’s program of naming and shaming firms who employed foreigners was outrageous, and she is now indelibly headlined as Amber Rudderless.

That is unfair. Rudd wouldn’t have a hand on the rudder that was not guided from the top by May.

When she replaced Cameron in 10 Downing Street, May’s reputation was fortified by the fact that she had survived six years as home secretary, an office that had destroyed many a prime minister contender in the past.

It now seems that the qualities that made her the longest serving home secretary for 60 years are not the same qualities that are required to effectively manage the crisis that Brexit has created. In the Home Office she displayed the talents of a controlling bureaucrat, depending on a small cadre of carefully chosen advisors and navigating herself clear of the Conservative party’s fratricidal tendencies. In Downing Street all those tendencies are in naked play—with the mendacious Boris Johnson still calculating his chances of making it to prime minister.

May’s most costly blunder so far has been to disaffect the people who are not only her party’s major source of funding but whose mercantile skills drive the economic performance of the country—business and financial leaders who are mostly based in London.

Mark Carney, the Canadian-born governor of the Bank of England warned before the fatal referendum on leaving Europe was held that it was inward investment that really kept the country afloat—foreigners investing in British businesses and financial services. Carney said that, ultimately, the economy depended on “the kindness of strangers.”

May has a tin ear when it comes the precariousness of the economy. One observer, Charles Grant of the Centre for European Reform, told the Financial Times: “Theresa May’s closest advisers may not be experts on the European Union, on economics, on geopolitics and diplomacy. Decisions that are going to affect Britain for years are being taken by people who are not experts.”

The sell-off of sterling caught May by surprise. Her ministers have tried to spin it by saying that the pound was overvalued and that its depreciation will boost exports by lowering their price. This is hokum. The other side of the coin is that the price of everything that Britain imports is going up. Brexit supporters are beginning to get rattled as they see the immediate effects, in the price of gas at the pump and food in the supermarket.

They are also witnessing the antics of Boris Johnson with new alarm. A few days ago, in his first House of Commons debate as foreign secretary, he faced angry questions about what the government could do to stop the carnage in Aleppo. His advice: people should demonstrate outside the Russian Embassy in London.

That is, apparently, the new foreign policy of Little England. A little gesture.

Lord Palmerston must be spinning in his grave.