Deputy Prime Minister Angela Rayner has dismissed an SNP jibe over the row over Labour Party volunteers campaigning in the US presidential election.

Donald Trump’s campaign has filed a complaint alleging Labour has broken US election rules on foreign interference by sending activists to campaign for his Democratic Party opponent, Kamala Harris.

Rayner told MPs that “people in their own time often go on campaigns”, adding that “it happens in all political parties”, during Prime Minister’s Questions.

She was standing in for Sir Keir Starmer, who has also played down the row while on his way to Samoa for the Commonwealth Heads of Government Meeting, which King Charles will open on Friday.

Rayner was responding to a question from Stephen Flynn, leader of the SNP at Westminster, who invited her to join him “in applauding the brave Labour staff members who travelled across the Atlantic to campaign against Donald Trump?”

The deputy PM replied: “People in their own time often go and campaign, and that’s what we’ve seen.

“It happens in all political parties, people go and campaign and they do what they want to do with their own time, with their own money.”

The row over campaigning was sparked by a now-deleted social media post from Labour’s head of operations, Sofia Patel, that she had about 100 current and former party staff heading to America before polling day.

The LinkedIn post said she had “10 spots available” for anyone willing to travel to North Carolina to campaign for Harris, adding “we will sort your housing”.

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

Labour Party sources insist no one has done anything wrong, but there is concern about whether the row could impact the so-called “special relationship” between the UK and US should Trump win the election on 5 November.

The Trump campaign complaint to the Federal Election Commission flags that senior Labour Party staff attended the Democratic convention in Chicago and met Harris’s campaign team, naming Morgan McSweeney, the prime minister’s chief of staff, and Matthew Doyle, Downing Street director of communications.

Deborah Mattinson, Sir Keir’s former director of strategy, was also named as someone who travelled to Washington in September to brief Harris’s campaign on Labour’s election-winning approach.

It is understood from Labour officials that Labour met McSweeney’s costs, while Doyle was hosted by the Progressive Policy Institute, a US think tank.

But the officials said it would be wrong to suggest either man had advised or assisted the Harris campaign, adding that Labour sends a delegation to each Democratic convention.

Officials also pointed out that Mattinson left the Labour party staff after July’s general election in the UK.

Sir Keir briefly addressed the issue during his plane journey, telling reporters: “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.”

He denied the row would impact his relationship with Trump, reminding reporters the two had dinner together at Trump Tower in New York last month.

The Prime Minister’s deputy spokesperson stressed that the UK would always have “a deep and strong relationship with the US as our closest ally” whoever won the election.

She was not aware of any plans for government ministers to speak to Trump’s campaign team, but Sir Keir and Trump had discussed “the long-standing friendship” between the two nations during their New York dinner, she said.

“It is a special relationship which has endured for over a century with leaders of all political stripes, and that will always be the case,” she added.

Defence Secretary John Healey suggested the Trump campaign was “creating controversy” ahead of the presidential election.

However, Nigel Farage, the Reform UK leader and Trump supporter, told the BBC he believed the wording of the LinkedIn post breached US election law, saying the rules were “very, very clear”.

Farage, who has travelled to the US to support his friend on multiple occasions, said: “The ad didn’t say you’ll be going in your own free time, didn’t say you’ll have to pay your own air fare, which at the moment, by the way, are very, very expensive, it said you’re going to have free accommodation.

“If you look at the wording of that advert there is little doubt that is against American election law.”

Filings with the US Department of Justice reveal that Farage himself has received help three times since his election as an MP in July from a PR firm based in Pennsylvania, including with hotel costs on a trip to the USA.

The company, Capital HQ LLC, is run by Alexandra Preate, who used to be an aide to Trump’s former strategist Steve Bannon.

The filings show the firm paid more than $3,500 (£2,700) for Farage’s accommodation at the Republican National Convention in Milwaukee in July.

It also helped with his “perception management”, as well as public relations, travel and logistics.

Capital HQ disclosed it had also assisted with his appearance on a Fox News business programme in July, in which he was outspoken in support of Trump’s election prospects.

It also spoke to him in August about an “upcoming trip to the United States”.

The filings were made under US laws requiring anyone who acts on behalf of foreign “principals” engaged in political activity, such as seeking to influence policy or public opinion there, to register with the federal government.

The Clacton MP has declared £32,836 he separately received from a donor for flights and accommodation for a visit to the United States in July.

Asked about this on BBC’s Politics Live programme, Farage said he “hopped on somebody else’s plane, they gave me a free lift”, adding that he had declared it and “didn’t campaign at all”.

“I went in a purely personal capacity to offer my support after the first assassination attempt… as a friend of his and the family”.

Sir Keir Starmer has said he wants to focus on the future of the Commonwealth, after ruling out compensation for the UK’s historical role in the slave trade.

All three candidates to become the next head of the 56-nation organisation have called for reparations for countries that were affected by slavery.

A group of Caribbean nations has indicated it will push for the issue to be discussed at a summit of the bloc’s leaders in Samoa this week.

But the UK prime minister said he wanted to address “current future-facing challenges” rather than “spend a lot of time on the past”.

Sir Keir’s government has ruled out making slavery reparations, continuing a longstanding British stance on the subject.

Downing Street has also said Sir Keir will not be apologising for Britain’s role in the transatlantic slave trade.

Speaking to reporters on his way to Samoa, the Labour leader said there was “no question” that slavery was “abhorrent”.

But he added that he wanted to focus on the challenges that Commonwealth countries were “facing right now” rather than what “will end up being very, very long endless discussions about reparations on the past”.

“This is about stance really, looking forward rather than looking backwards,” he said.

The Atlantic slave trade saw millions of Africans enslaved and forced to work, especially on plantations in the Caribbean and the Americas, for centuries from around 1500.

The British government and the monarchy were prominent participants in the trade, alongside other European nations.

The UK also played a key role in ending the trade through Parliament’s passage of a law to abolish slavery in 1833.

Reparations are broadly recognised as compensation for something that was deemed wrong or unfair, and can take many forms.

LinkedIn: the social network for CVs, apparently motivational corporate messages and – as of late last night – transatlantic diplomatic spats.

When Sofia Patel, the Labour Party’s head of operations, posted on the site last week that she was coordinating nearly 100 current and former party officials to campaign in battleground states in the final weeks of the US presidential election, she surely could not have imagined that she would provoke a legal complaint filed in Florida.

In a formal complaint to the Federal Election Commission (FEC), the Trump presidential campaign’s deputy general counsel declared: “When representatives of the British government previously sought to go door-to-door in America, it did not end well for them.”

Last week, he noted, was the 243rd anniversary of the Battle of Yorktown – a military victory which ensured the United States’ enduring independence from “Great Britian” [sic].

Bombastic as that may sound, it’s hardly of trivial interest that a Labour Party that has conspicuously sought to improve its ties to Trump and his team is now being formally accused of “blatant foreign interference” on behalf of his opponent, Kamala Harris.

So what’s behind all this?

Under the FEC rules, foreign volunteers on US campaigns are permissible, as long as they are just that – volunteers – and are not compensated for their work.

That is exactly what Labour says these operatives were: volunteers. While Patel’s LinkedIn post told those interested in campaigning that “we will sort your housing”, it is being argued that this was imprecise language.

Sir Keir Starmer told reporters last night that Labour officials going to the US to campaign are “doing it as volunteers, they’re staying I think with other volunteers over there”.

There is a question over what exactly Patel meant by saying she had “10 spots available” for people willing to campaign in North Carolina.

Did that entail travel costs to get there being covered? Even if it did, Labour are adamant that they did not pay.

But arguably the more pertinent charge, diplomatically at least, is the allegation that the Labour Party as an institution is formally coming to the aid of the Democrats.

This is being denied too. Labour sources say that Ms Patel was, in her spare time, organising party officials to go out to the US in their spare time.

That was the argument from Steve Reed, the environment secretary, this morning: “It’s up to private citizens how they use their time and their money”.

And of course, it’s not surprising that those on the left of politics here would want the Democratic candidate to win the US election, just as at least one recent former Conservative special adviser is currently in a swing state campaigning for Trump.

There’s another element to this, too. The British political world is utterly obsessed with American politics, even if it is an almost totally unrequited passion.

Every four years, British politicos stream across the Atlantic for a taste of campaigning on a far bigger canvas.

There are numerous examples. Earlier this summer Nigel Farage, the Reform UK leader, was at the Republican convention just days after his election as an MP, as was Liz Truss, the former prime minister, just days after she lost her seat.

Penny Mordaunt, the former Conservative cabinet minister, worked for George W Bush before she became an MP. Liam Fox, another ex-Conservative MP, has had ties with senior figures in the Republicans for a number of years.

Not that the parties on either side of the Atlantic always match up neatly.

In January 2020, I was shadowing a small group of canvassers for Joe Biden in the New Hampshire presidential primary, when I realised that one of them was Sir Simon Burns, the former Conservative MP for Chelmsford.

In recent weeks Sir Robert Buckland, who lost his seat as a Conservative at the general election, has been in the US campaigning for Harris.

Be all that as it may, it’s undeniable that this is a seriously awkward spot for the Labour government to find itself in, exactly two weeks before Starmer could well be placing a phone call congratulating President-Elect Trump.

In opposition and in government, Labour officials have invested significant energy in trying to forge links to Trump and his allies.

David Lammy, the foreign secretary, spent time with JD Vance, the senator from Ohio who then became Trump’s candidate for vice-president.

Diplomats were delighted with how quickly Starmer managed to speak on the phone to Trump after the failed assassination attempt on him in July, and just a few weeks ago they met for the first time over dinner at Trump Tower in New York.

Senior Labour figures believe that this legal wrangle is not really a rebuke of that approach, but instead just straightforward politicking from the Trump campaign, who are eager to use the Labour volunteers as a way to bash the Harris campaign in the crucial final stretch.

They need to be right.

Because if they are wrong, then this may not be a mere passing awkwardness, but a dispute threatening the most important diplomatic relationship any British prime minister has.