Donald Trump’s campaign has accused Sir Keir Starmer’s Labour Party and Kamala Harris of election interference.
The Republican candidate’s team filed a complaint to the Federal Election Commission, the US agency that oversees the country’s election laws.
It accused Labour of making “illegal foreign campaign contributions and interference in our elections”.
Sir Keir’s party was branded “far left” in a strongly worded Trump-Vance campaign statement headlined “The British Are Coming”, which accused Labour of inspiring “Kamala’s dangerously liberal policies and rhetoric”.
It comes after it emerged last week that more than 100 current and former Labour staff were heading to the US to campaign for the Democrats ahead of the ballot on November 5.
Mr Trump’s campaign co-manager Susie Wiles said: “In two weeks, Americans will once again reject the oppression of big government that we rejected in 1776.
“The flailing Harris-Walz campaign is seeking foreign influence to boost its radical message – because they know they can’t win the American people.
“President Trump will return strength to the White House and put America, and our people, first.
“The Harris campaign’s acceptance and use of this illegal foreign assistance is just another feeble attempt in a long line of anti-American election interference.”
Activists from Sir Keir’s party were due to travel to swing states Nevada, North Carolina, Pennsylvania and Virginia to canvass for Democrat candidate Ms Harris.
It is understood the trips were for individuals in a personal capacity and were not organised or funded by Labour.
But the revelation sparked an intense backlash from Republicans, as well as politicians in the UK including Reform leader Nigel Farage, former PM Liz Truss and Ashfield MP Lee Anderson.
Labour was contacted for comment.