LONDON — Evoking the Battle of Yorktown and misspelling the word Britain, former President Donald Trump issued a remarkable legal complaint against the United Kingdom’s ruling Labour Party late Tuesday, accusing it of “blatant foreign interference” in the U.S. election in favor of Vice President Kamala Harris.

Trump’s team asked the Federal Election Commission to investigate after a senior Labour figure posted a rallying cry for current and former staffers to travel to battleground states and campaign for Harris ahead of the Nov. 5 vote.

British Prime Minister Keir Starmer said Wednesday his party had done nothing wrong. Party members often travel to the United States ahead of elections to help out their Democratic bedfellows, he said, but added that this was voluntary rather than party-led, and therefore does not contravene American election law.

Nevertheless, if the FEC agrees with Trump — that Labour and Harris are guilty of flouting foreign interference rules — the agency could issue big fines.

Either way, if Trump wins next month the filing paves the way for a deeply awkward start to the partnership with Britain’s Labour — who he described as “far left” despite the party’s notably centrist shift in recent years. It would also appear to signal he has no plans to soften the bruising and norm-busting treatment he meted out to Washington’s closest allies during his first term.

“When representatives of the British government previously sought to go door-to-door in America, it did not end well for them,” wrote Trump campaign lawyer Gary Lawkowski. “This past week marked the 243 anniversary of the surrender of British forces at the Battle of Yorktown, a military victory that ensured that the United States would be politically independent of Great Britian [sic]. It appears that the Labour Party and the Harris for President campaign have forgotten the message.”

When Trump’s letter dropped, Starmer was on a 28-hour flight to the Pacific island of Samoa, where he will attend the Commonwealth Heads of Government Meeting.

He denied Labour had broken any laws, saying it has volunteers “who have gone over pretty much every election,” NBC News’ British partner Sky News, which is on the plane, reported.

“They’re doing it in their spare time, they’re doing it as volunteers, they’re staying, I think, with other volunteers over there,” he said, adding that he had “established a good relationship” with Trump. “That’s what they’ve done in previous elections, that’s what they’re doing in this election and that’s really straightforward.”

In an email to NBC News, a Labour spokesperson reiterated that it was “common practice for campaigners of all political persuasions from around the world to volunteer in U.S. elections.” The spokesperson said that “where Labour activists take part, they do so at their own expense, in accordance with the laws and rules.”

The crux of Trump’s complaint is a now-deleted LinkedIn post from Labour’s head of operations, Sofia Patel, in which she said nearly 100 “Labour Party staff” were traveling to North Carolina, Pennsylvania, Virginia and Nevada. There were 10 “spots” left in North Carolina, she posted, and “we will sort your housing.”

It’s that offer that Trump’s team says constitutes foreign interference — alleging the “we” refers to the Labour Party itself.

Foreign nationals are allowed to volunteer during election campaigns but must not participate in any decision-making process or incur expenses of more than $1,000 per candidate. Any British volunteer whose flights, accommodation and daily expenses exceed this amount could be in breach of the law.

Trump’s legal letter also highlights that Starmer’s chief of staff, Morgan McSweeney, and communications director Matthew Doyle traveled to August’s Democratic National Convention in Chicago. It is not uncommon nor controversial for foreign political allies to travel to these summits, however.

Former Starmer advisers have briefed campaign staffers for Harris, who has also adopted some of the same slogans — “turn the page” and “end the chaos”

Trump is no stranger to wading into other countries’ politics himself, including Britain’s. In 2019, he called populist hard-right lawmaker Nigel Farage’s radio show to praise Prime Minister Boris Johnson and lambast his opponent, Jeremy Corbyn.

Washington’s friends are well used to Trump’s brusque style, but the letter could be a significant event in the transatlantic relationship because it hints at how things may play out should Trump win.

President Joe Biden describes the U.K. as his “closest ally,” and British politicians are always eager to make the most of their “special relationship.” Starmer would never publicly bad-mouth the possible soon-to-be Leader of the Free World, but his center-left policies far more closely resemble those of Harris’ Democrats.

In 2016 the FEC fined the Australian Labor Party and the campaign of Bernie Sanders after the ALP paid for its delegates to campaign for the left-wing Democrat.

Help also goes the other way across the pond.

A year earlier, in 2015, Jim Messina and David Axelrod, both former aides to then President Barack Obama, were hired as advisors by Britain’s Conservative and Labour parties respectively.

Messina’s Conservatives came out on top.