Nigel Farage used nearly $42,000 (£33,000) of UK donor cash to help support Donald Trump in the US election – months before he complained about Labour activists volunteering for Kamala Harris.

After he was elected as an MP, the Reform UK leader missed the King’s Speech to travel to Wisconsin in July to attend the Republican National Convention (RNC).

He publicly admitted his trip was intended “to support my friend Donald Trump at the RNC”, adding “we all have a duty to support and defend democracy.”

Eminem introduces Obama in Michigan before ex-president raps ‘Lose Yourself’ to crowd

It comes after Mr Trump’s campaign filed a complaint with the Federal Election Commission (FEC), calling for an investigation into whether around 100 UK Labour Party activists and staff volunteering for Ms Harris’ campaign was a breach of US election rules.

Under federal law, the travel expenses of a volunteer are considered a donation to the party they work for if they exceed $1,000 (£770) in one election.

When it was first revealed that Labour activists had been volunteering for Ms Harris, Mr Farage said: “This is direct election interference by the governing Labour Party, and particularly stupid if Trump wins. Who is paying for all of this?”

Mr Farage’s trip was paid for by Christopher Harborne, a British tech investor based in Thailand.

Mr Farage declared on his register of members interests that the flights and accommodation for the trip came to £32,836.

Former Prime Minister Liz Truss also attended the convention – but as she was not an MP at the time, she did not have declare the cost of the trip.

Both of them also attended the Conservative Political Action Conference (CPAC) in Washington DC in March – and both endorsed Mr Trump to be the next US President during their speeches from the stage.

Mr Farage said: “[Trump] needs from all of us, our absolute, total commitment and our unwavering support for him as a man. Unwavering support.”

In her speech, earlier the same day, Ms Truss said: “Of course, we need a Republican back in the White House. We need it desperately.”

Despite taking place within the 12 months before his election, Mr Farage has not declared anything related to the CPAC trip on his register.

But Ms Truss declared a donation from the convention’s organisers of £1,465 towards her flights and accommodation.

In a Telegraph article, cited as evidence in the Trump campaign’s complaint, constitutional law expert Lawrence Otter is reported as saying a campaign and any activist who spends more than $1,000 supporting them could end up with a “substantial” fine by the FEC.

“The cost of getting here by air, if it is less than $1,000 it would be okay, but anything more than that it becomes very problematic in my opinion,” he told the Telegraph.

“I think the campaign could be sanctioned, probably through a fine, which could be substantial.”

Mr Farage was given a “national interest” exemption to the US Covid-19 border lockdown in 2020, to allow him entry into the country to appear at a Trump campaign rally in Tulsa, Oklahoma.

He returned to the States in October that year, during the last weeks of the campaign, to appear at another rally alongside the then-President in Arizona.