Britain’s new government found itself on a collision course with former President Donald J. Trump on Wednesday after his campaign filed a complaint that accused the governing Labour Party of interfering in the American presidential election by recruiting volunteers to canvass for Vice President Kamala Harris in battleground states.
In a letter to the Federal Election Commission dated Monday, a lawyer for the Trump campaign said that Labour’s recruitment of volunteers, as well as recent meetings in which Labour officials offered advice to the Harris campaign, constituted “blatant foreign interference” in the election.
Prime Minister Keir Starmer brushed off the accusations, saying that Labour activists had worked on an unpaid basis in multiple American elections. Mr. Starmer, who had dinner with Mr. Trump during a recent visit to New York, said the issue would not poison their relations if Mr. Trump were elected.
“As prime minister of the United Kingdom, I will work with whoever the American people return as their president in their elections, which are very close now,” Mr. Starmer told reporters on his way to a diplomatic gathering in Samoa.
Mr. Starmer said that Labour activists were volunteering in their spare time, not as employees of the party. The party said they would be expected to cover their own travel expenses and lodging, which is typically provided by Democratic campaign volunteers in the United States. “That’s really straightforward,” Mr. Starmer said.
But the Trump campaign’s lawyer, Gary Lawkowski, argued in the complaint that the donation of time and services by British volunteers amounted to “illegal foreign national contributions” to the Harris campaign. He also cited conversations between senior Labour strategists, including Morgan McSweeney, who is now Mr. Starmer’s chief of staff, and advisers to Ms. Harris.
“When representatives of the British government previously sought to go door-to-door in America, it did not end well for them,” Mr. Lawkowski wrote, citing the recent 243rd anniversary of the surrender of British troops after the Battle of Yorktown during the Revolutionary War. “It appears the Labour Party and the Harris for President campaign have forgotten the message.”
Mr. Trump himself has not addressed the topic of the Labour volunteers. But he is no stranger to trans-Atlantic politicking — in either direction.
As president in 2019, Mr. Trump called into a London radio show hosted by Nigel Farage, a right-wing political figure, to offer full-throated support for Boris Johnson, who was then prime minister and had just called a general election. He also sharply criticized the Labour leader at the time, Jeremy Corbyn.
“He’d be so bad, he’d take you in such a bad way,” Mr. Trump said of Mr. Corbyn. “He’d take you into such bad places.”
An aggrieved Mr. Corbyn posted on social media at the time, “Donald Trump is trying to interfere in Britain’s election to get his friend Boris Johnson elected.”
Mr. Farage, who now holds a seat in Parliament and heads an anti-immigrant party, Reform U.K., has also campaigned for Mr. Trump. In the final week of Mr. Trump’s failed re-election campaign against President Biden in 2020, Mr. Trump welcomed Mr. Farage to the stage at a rally in Goodyear, Ariz.
Mr. Farage initially announced that he would skip the most recent British general election because he wanted to focus on helping Mr. Trump win back the White House. “I intend to help with the grass-roots campaign in the U.S.A. in any way that I can,” he posted on social media, before reversing course a week later.
Mr. Starmer has tried to steer clear of the American election, though he met with the former president while in the United States to attend the United Nations General Assembly in September. He has not spoken publicly about the meeting, except to say that he and Mr. Trump had a “good relationship.”
Allies of Mr. Trump draw a distinction between expressing support for a candidate, which they say is exercising free speech, and organized canvassing. His campaign cited a volunteer effort organized by Australia’s Labor Party in 2016 to support the campaign of Senator Bernie Sanders of Vermont.
The Election Commission found that those efforts violated a prohibition on foreign contributions. But unlike Britain’s Labour Party, the Australian party paid for the travel expenses of its volunteers, as well as giving them a daily stipend.
The Trump campaign’s letter appeared to have been provoked by a LinkedIn post, which has since been deleted, by Sofia Patel, a senior Labour Party operative. “I have nearly 100 Labour Party staff (current and former) going to the U.S. in the next few weeks heading to North Carolina, Nevada, Pennsylvania and Virginia,” the post read. “I have 10 spots available for anyone available to head to the battleground state of North Carolina — we will sort your housing!”
The campaign also cited meetings between Labour and advisers to Ms. Harris, which it claims led to “generously borrowed language and themes from prominent Labour Party officials.”
In an interview last month, Jonathan Ashworth, a former Labour member of Parliament, said that he and other officials, including Mr. McSweeney and Matthew Doyle, Mr. Starmer’s communications adviser, had spoken with Harris officials and other Democrats at the Democratic National Convention in Chicago.
“There was huge interest in how we won our campaign,” said Mr. Ashworth. He said that on immigration, they had advised the Harris officials to emphasize a need for robust law enforcement. Mr. Starmer had promised during his own campaign to break up the gangs that traffic migrants across the English Channel.
Mr. Ashworth said he had also warned Democrats not to be complacent about the anger among pro-Palestinian voters over the Biden administration’s stance on the war in Gaza. He spoke from personal experience: He lost his seat in the recent election because of a backlash against Labour, which critics said was too slow to condemn Israel’s killing of Palestinian civilians in the military campaign.
“The anger was not captured in the polling,” Mr. Ashworth said. “They’ve got to make sure people don’t stay home because of Gaza.”
Labour Party officials said neither Mr. McSweeney nor Mr. Doyle were in Chicago to advise or assist the Harris campaign. The party picked up Mr. McSweeney’s expenses, while Mr. Doyle’s were covered by the Progressive Policy Institute, a center-left think tank in Washington.
Political analysts in Britain said the dispute appeared to be generated largely to paint Ms. Harris as an extreme leftist. In a statement on Tuesday, a top Trump campaign aide, Susie Wiles, said, “the far-left Labour Party has inspired Kamala’s dangerously liberal policies and rhetoric.”
Labour activists have long traveled to the United States during presidential campaigns. Natalie Fleet, a newly elected Labour member of Parliament, recalled canvassing for Hillary Clinton as a young volunteer in Ohio in 2016.
There is also a long history of connections between British and American political advisers, sometimes producing strange bedfellows: In 2013, Jim Messina, a Democratic consultant and campaign manager for President Barack Obama, signed on as a consultant to Britain’s Conservative Party. His former colleague David Axelrod was advising Labour.
“English politics is not analogous to U.S. in their political positions,” Mr. Messina said at the time. “The Conservatives are not Republicans in the United States.”
