LONDON, Oct 23 (Reuters) - Donald Trump's campaign has accused British Prime Minister Keir Starmer's Labour Party of "blatant foreign interference" in the U.S. presidential election after some volunteers travelled to help campaign for Kamala Harris.

The Republican candidate's camp has filed a complaint with the Federal Election Commission in Washington, calling for an investigation into what it termed apparently illegal contributions from Labour to the Harris campaign.

British political volunteers have long travelled to the U.S. ahead of elections, with activists of the centre-left Labour Party typically supporting the Democrats, its sister party, and Conservatives backing the Republicans.

British officials, who asked not to be named, told Reuters that some senior Labour advisers travelled to meet Democrat strategists in recent months, on the back of their landslide victory in the British election in July.

One topic they discussed was how Labour won back almost all the former industrialised areas that abandoned them in 2019.

Labour leader Starmer denied that the complaint would damage relations with Trump if the former president wins again on Nov. 5, saying Labour supporters were volunteering in their own time.

But the complaint is a potential complication.

Trump, who is close to Britain's right-wing politician Nigel Farage and previously had good ties with former prime minister Boris Johnson, had praised Starmer when the two met in September at Trump Tower.