The investigation into links between Trump campaign officials and Russia has requested documents from a data firm which worked on both the 2016 presidential election and Brexit, said US media.

Robert Mueller, who is leading the federal probe, asked Cambridge Analytica to hand over the emails of any employee who worked to support Donald Trump’s 2016 election win, the Wall Street Journal reports.

The special counsel’s request, which the firm reportedly voluntarily complied with in the autumn, suggests the investigation is now probing the Trump campaign’s data operations.

And it could also have repercussions in Britain, and particularly for Leave.EU, a campaign group during the EU referendum, which is under investigation by the Electoral Commission over alleged “impermissible” services from the data firm.

Robert Mercer, founder of Cambridge Analytica and co-owner of right-wing news organisation Breitbart, allegedly directed the data firm to provide expert advice to Leave.EU, which received prominent support from Nigel Farage.

Leave.EU’s communications director, Andy Wigmore, told The Observer Mr Mercer had offered his company’s services for free. “They were happy to help because Nigel is a good friend of the Mercers,” Mr Wigmore said.

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In March, Mr Farage thanked Breitbart and Steve Bannon, Mr Trump’s former chief strategist and a director at Cambridge Analytica, for “hugely” helping the vote for Brexit.

The firm reportedly harvested data from UK voters’ Facebook profiles to help decide how to target them with tailored Brexit campaign messages. Similar methods were employed to help the Trump campaign.

However, Leave.EU failed to inform the electoral commission about the firm’s work. All services worth more than £7,500 must be declared.

In April, the Electoral Commission said in a statement: “The Electoral Commission has begun an investigation into Leave.EU’s EU Referendum spending return. This followed an assessment which concluded that there were reasonable grounds to suspect that potential offences under the law may have occurred.

“The investigation is focused on whether one or more donations – including of services – accepted by Leave.EU was impermissible; and whether Leave.EU’s spending return was complete.”

Alexander Nix, chief executive of Cambridge Analytica, said in a speech in November he had asked the office that arranges his engagements to contact Julian Assange, founder of whistle-blowing organisation WikiLeaks, in “early June 2016”.

What experts have said about Brexit Show all 11 1 /11 What experts have said about Brexit What experts have said about Brexit Chancellor of the Exchequer Philip Hammond The Chancellor claims London can still be a world financial hub despite Brexit “One of Britain’s great strengths is the ability to offer and aggregate all of the services the global financial services industry needs” “This has not changed as a result of the EU referendum and I will do everything I can to ensure the City of London retains its position as the world’s leading international financial centre.” Reuters What experts have said about Brexit Yanis Varoufakis Greece's former finance minister compared the UK relations with the EU bloc with a well-known song by the Eagles: “You can check out any time you like, as the Hotel California song says, but you can't really leave. The proof is Theresa May has not even dared to trigger Article 50. It's like Harrison Ford going into Indiana Jones' castle and the path behind him fragmenting. You can get in, but getting out is not at all clear” Getty Images What experts have said about Brexit Michael O’Leary Ryanair boss says UK will be ‘screwed’ by EU in Brexit trade deals: “I have no faith in the politicians in London going on about how ‘the world will want to trade with us’. The world will want to screw you – that's what happens in trade talks,” he said. “They have no interest in giving the UK a deal on trade” Getty What experts have said about Brexit Tim Martin JD Wetherspoon's chairman has said claims that the UK would see serious economic consequences from a Brexit vote were "lurid" and wrong: “We were told it would be Armageddon from the OECD, from the IMF, David Cameron, the chancellor and President Obama who were predicting locusts in the fields and tidal waves in the North Sea" PA What experts have said about Brexit Mark Carney Governor of Bank of England is 'serene' about Bank of England's Brexit stance: “I am absolutely serene about the … judgments made both by the MPC and the FPC” Reuters What experts have said about Brexit Christine Lagarde IMF chief urges quick Brexit to reduce economic uncertainty: “We want to see clarity sooner rather than later because we think that a lack of clarity feeds uncertainty, which itself undermines investment appetites and decision making” Getty Images What experts have said about Brexit Inga Beale Lloyd’s chief executive says Brexit is a major issue: "Clearly the UK's referendum on its EU membership is a major issue for us to deal with and we are now focusing our attention on having in place the plans that will ensure Lloyd's continues trading across Europe” EPA What experts have said about Brexit Colm Kelleher President of US bank Morgan Stanley says City of London ‘will suffer’ as result of the EU referendum: “I do believe, and I said prior to the referendum, that the City of London will suffer as result of Brexit. The issue is how much” What experts have said about Brexit Richard Branson Virgin founder believes we've lost a THIRD of our value because of Brexit and cancelled a deal worth 3,000 jobs: We're not any worse than anybody else, but I suspect we've lost a third of our value which is dreadful for people in the workplace.' He continued: "We were about to do a very big deal, we cancelled that deal, that would have involved 3,000 jobs, and that’s happening all over the country" Getty Images What experts have said about Brexit Barack Obama US President believes Britain was wrong to vote to leave the EU: "It is absolutely true that I believed pre-Brexit vote and continue to believe post-Brexit vote that the world benefited enormously from the United Kingdom's participation in the EU. We are fully supportive of a process that is as little disruptive as possible so that people around the world can continue to benefit from economic growth" Getty Images What experts have said about Brexit Kristin Forbes American economist and an external member of the Monetary Policy Committee of the Bank of England argues that the economy had been “less stormy than many expected” following the shock referendum result: “For now…the economy is experiencing some chop, but no tsunami. The adverse winds could quickly pick up – and merit a stronger policy response. But recently they have shifted to a more favourable direction” Getty

After reading a newspaper report about WikiLeaks’ plans to release emails from Hillary Clinton’s presidential campaign, Mr Nix asked Mr Assange if he “might share that information with us”. US intelligence agencies later concluded the emails had been stolen by Russian intelligence and handed to the website.

Mr Nix’s request came at the same time Cambridge Analytica started working for the Trump campaign, the Wall Street Journal reported. Mr Assange said he denied the request.

Adam Schiff, the senior Democrat on the House Intelligence Committee, has said the connection between the data firm and WikiLeaks is of “deep interest” to the committee, which is also investigating Russian interference into the 2016 presidential election.