LONDON — It’s always awkward when guests drop by right in the middle of an intense family argument, which might make for some uncomfortable moments when President Obama travels to Britain next week.
A rising number of Britons say they are offended that the U.S. president will try to persuade them to stay in the European Union, just as a poll indicates the “Out” forces have pushed into the lead in the national vote.
“If the American people aren’t happy with foreign heads of state or politicians telling them how to vote, then they shouldn’t be happy with their head of state lecturing other countries,” said Rory Broomfield, director of the “Better Off Out” campaign to leave the European Union.
He described Mr. Obama’s pressure as “sort of 1776 in reverse.”
Mr. Obama’s intervention in the debate has been so contentious that more than 100 members of Parliament signed an open letter last month essentially requesting that he butt out.
“It has long been the established practice not to interfere in the domestic political affairs of our allies and we hope that this will continue,” the letter read. “While the U.S. administration may have a view on the desirability or otherwise of Britain’s continued membership of the EU, any explicit intervention in the debate is likely to be extremely controversial and potentially damaging.”
The “Brexit” referendum is scheduled for June 23. If approved, Britain will begin negotiations on the terms of ending its 43-year ties to the European Union. Those talks could take two years, with unknown political and economic effects, and would certainly undermine the already shaky image of the European Union as a global force that speaks reliably for the Continent’s interests.
Dutch voters this month rejected an EU-sponsored free trade deal with Ukraine. The vote was viewed as a protest of “European elites” who want to take down trade and investment barriers without considering the effects on their citizens.
Brexit advocates similarly argue that EU regulations are weighing down the British economy and that European immigrants, especially cheap labor from Eastern Europe, are undercutting local job markets and wage levels.
Among Mr. Obama’s most prominent critics is London Mayor Boris Johnson, who is widely seen as a leading contender to succeed Prime Minister David Cameron. The colorful mayor has called Mr. Obama’s intervention in British democracy “a piece of outrageous and exorbitant hypocrisy.”
Mr. Obama’s open advocacy is even more striking given the closeness of the polls and the unpredictability of the vote.
A compilation of recent polls puts the race at a dead heat. An online poll released Tuesday by ICM Research Ltd. put the “Out” camp up by 45 percent to 42 percent, with 12 percent of voters still making up their minds.
“Most polls continue to suggest that it’s a very tight contest, with neither side able to gain a decisive lead,” ICM pollster Jennifer Bottomley told the Reuters news agency.
Bucking many in his Conservative Party hierarchy, Mr. Cameron has come out in favor of continued EU membership and will stand side by side with Mr. Obama.
Before the Brexit debate, Mr. Obama was popular among U.K. voters. A Pew Research Center survey in June found that 76 percent of Britons had confidence in Mr. Obama to “do the right thing regarding world affairs,” compared with 22 percent who did not.
Past U.S. administrations have tacitly supported British membership in the European Union, though their persuasion was couched in diplomatic calls for a strong and united Europe.
Mr. Obama’s move to weigh in explicitly on the June referendum marks one of the few times in history that sitting politicians — in either the U.S. or the United Kingdom — have sought to directly influence an issue of domestic policy across the Atlantic, said Anglo-American relations analyst Alan Dobson, an honorary professor at Swansea University in Wales.
“It’s certainly a departure from normal diplomatic practice. He’s taking a stance that has direct implications for domestic politics,” said Mr. Dobson. “It strikes me as being out of character.”
Some see Mr. Obama’s visit, part of a trip that will also include stops in Germany and Saudi Arabia, as partial payback for Mr. Cameron’s open and equally criticized support in Washington last summer in support of the nuclear deal with Iran. The British prime minister acknowledged that he personally lobbied individual members of Congress in January 2015 to oppose a bill that would threaten tough economic sanctions against Iran as Mr. Obama was trying to nail down the nuclear deal with Tehran.
Mr. Obama was far more restrained during the 2014 Scottish independence referendum. He merely said he valued the traditional U.S.-British alliance and wanted Britain to be a strong partner, Mr. Dobson said.
Those who want to stay in the European Union said Britain’s membership makes it a far more effective player diplomatically in its backyard. Mr. Obama has expressed similar sentiment, saying the United Kingdom inside the European Union gives him “much greater confidence about the strength of the tran-Atlantic union.”
But the president will also undoubtedly tout the economic benefits of Britain’s role as a bridge between the English-speaking U.S. and the Continental powers across the English Channel. “The economic relationship between the U.K. and U.S. is really quite phenomenal and all that, of course, is enriched by Britain being in the EU,” Mr. Dobson said.
The White House has been coy about how strong Mr. Obama’s message will be.
A “senior White House official” in a background briefing this month, after the trip was officially confirmed, said the president “will respect the sovereignty of the U.K. and the right of the British people to make that determination” on EU membership.
But, the aide added, “when the president is taking questions from the press corps, I wouldn’t be surprised if this is at that point considered a newsworthy topic that comes up.”
The European Union began in the 1950s as a post-World War II industrial agreement among six European countries. Engineered with U.S. financial and political support, it sought to make another war between the great European powers impossible through closer trade and cultural integration. Since then, the European Union has swelled to include 28 countries, developed a single currency (one not used in Britain), and brought former Soviet-dominated East European countries into the fold. London’s relatively late entry into the bloc in 1973 reflected the traditional British ambivalence about a too-close involvement in Continental affairs.
Although the Brexit referendum has divided Mr. Cameron’s Tories, the opposition Labor Party supports staying in the European Union and has warmly welcomed Mr. Obama’s visit.
“Members of the public will want to know what effect the referendum could have on the special relationship,” Alan Johnson, home secretary in the government of former Labor Prime Minister Gordon Brown, said in a statement. “President Obama is a unique and important voice in this debate and will help ensure voters are fully informed.”
Unlike more traditional trade pacts such as the North American Free Trade Agreement, EU membership means handing over significant decision-making powers to officials and unelected bureaucrats in Brussels. The U.S. president doesn’t understand that reality, Brexit advocates insist.
“We need the U.S. to understand that it’s like having an alien creed dictate laws,” Mr. Broomfield said.
The Brexit champion said he hopes Mr. Obama’s visit doesn’t start a trend in which U.S. and British politicians readily interfere in each other’s domestic politics. “I hope this doesn’t mark a watershed moment,” he said. “If something is broken, I hope it’s restored on both sides.”
But Mr. Dobson felt Mr. Obama’s visit wouldn’t set a troubling precedent or that it would harm relations between Mr. Obama and Mr. Johnson if he becomes prime minister when Mr. Cameron, as many expect, steps down before his government’s term formally ends in 2020.
The special relationship would live on “despite a temporary spat between Obama and a potential next prime minister,” Mr. Dobson said.