Prime Minister Sir Keir Starmer has sought to play down the significance of alleged interference by the Labour Party in the American presidential election.

The Trump Campaign has filed a complaint with the Federal Election Commission in Washington seeking an immediate investigation – after the Head of Operations for the Labour Party, Sofia Patel, posted on social media that she had “ten spots available” for anyone willing to travel to North Carolina to campaign for Kamala Harris, adding “we will sort your housing”.

She said she had around 100 current and former party staff heading to America before polling day.

The post, on LinkedIn, has since been deleted.

Foreign nationals are permitted to serve as volunteers on campaigns in the US as long as they are not compensated, according to Federal Election Commission rules.

The complaint from the Trump Campaign is both pointed and theatrical.

“When representatives of the British government previously sought to go door-to-door in America, it did not end well for them,” it read.

That is a matter-of-fact reference to US independence around 250 years ago.

On matters more contemporary it requests “an immediate investigation” into what it calls “blatant foreign interference”.

Speaking to reporters while flying to the Commonwealth Heads of Government Summit in Samoa in the south Pacific, the prime minister said: “The Labour Party has volunteers, [they] have gone over pretty much every election.

“They’re doing it in their spare time. They’re doing it as volunteers. They’re staying I think with other volunteers over there.”

The Trump Campaign letter to the Federal Election Commission also says: “Morgan McSweeney, the Prime Minister’s chief of staff, and Matthew Doyle, director of communications, attended the (Democratic) convention in Chicago and met with Ms Harris’ campaign team.

“Deborah Mattinson, Sir Keir’s director of strategy, also went to Washington in September to brief Ms Harris’ presidential campaign on Labour’s election-winning approach.”

Ms Mattinson no longer works for the Labour Party.

Party sources say Mr Doyle and Mr McSweeney went to the Democratic Convention in their own time, and that the Democratic Party didn’t pay their travel and accommodation costs.

It isn’t clear who did.

Asked if the row risked jeopardising his relationship with Donald Trump, the prime minister said “no” – pointing to the dinner the two men had together at Trump Tower in New York last month.

“We established a good relationship. We’re grateful for him for making the time… for that dinner,” Sir Keir said.

“We had a good, constructive discussion and, of course 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.”

Sir Keir has never met the Vice-President Harris, Trump’s Democratic rival.

But he has met President Biden several times since becoming prime minister in July.