A political strategist who worked on Sir Keir Starmer’s campaign has explained how she went to the US to share “lessons learned” with the Democrats following Labour’s election victory.

This week, the Trump campaign accused Labour of illegal interference after the party’s head of operations, Sofia Patel, posted on LinkedIn she was coordinating nearly 100 current and former party officials to campaign in battleground states.

Deborah Mattinson, who also worked with Tony Blair, Gordon Brown and Neil Kinnock, told Beth Rigby on the Electoral Dysfunction podcast she was asked to go to the US in September to talk to Democrats about Labour’s campaign by centrist Democratic thinktank Progressive Policy Institute.

She had already finished working for the Labour Party when she went to the US.

Ms Mattinson was speaking on Tuesday, ahead of the Trump campaign filing a complaint to the US federal electoral commission claiming there had been “interference” in the “form of apparent illegal foreign national contributions made by the Labour Party of the UK”.

Politics latest: Trump row over Labour ‘interference’

It references reports suggesting Labour strategists have been offering advice to Kamala Harris “about how to earn back disaffected voters and run a winning campaign from the centre left”.

The complaint also mentions a Telegraph report suggesting Morgan McSweeney, Sir Keir’s new chief of staff, and Matthew Doyle, his director of communications, “attended a convention in Chicago and met with Ms Harris’s campaign team”.

Ms Mattinson, who no longer works for Labour, said following the party’s landslide victory somebody she knew from the Progressive Policy Institute “got in touch with me…and said they would really like me to go over and share lessons learned with some of their colleagues in the Democrats”.

“I said, ‘fine’,” she added.

She said the thinktank funded that, including focus groups and polling “to understand who their hero voters were”.

“And that was what I did, that was what I took over there and shared with other Democratic organisations, with pollsters, with strategists on their side,” she said.

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Ms Mattinson said nobody from her team saw anybody from the Harris campaign, “but we talked to people that are working with them”.

She and those with her went over in September, in the week of the first and only debate between Ms Harris and Mr Trump, “so they were all down in Pennsylvania doing the debate”.

The strategist added the Progressive Policy Institute “was set up to collaborate between like-minded parties around the world, and that’s what they do”.

She said she is worried about what the impact of a Trump victory could be. “I’m worried about what that means for centre left parties around the world.”

Sir Keir has insisted his relationship with Mr Trump has not been jeopardised following the accusations of interference by the former president’s campaign.

The prime minister said on Tuesday he had “established a good relationship” with Mr Trump and said Labour Party volunteers “have gone over pretty much every election” but “in their spare time”.

The Labour Party has insisted it is not funding the travel or accommodation for activists.

Federal election rules stipulate foreign volunteers cannot spend more than $1,000 (£770) helping candidates.

A Labour Party spokesman said: “It is common practice for campaigners of all political persuasions from around the world to volunteer in US elections.

“Where Labour activists take part, they do so at their own expense, in accordance with the laws and rules.”