A Russian businessman “suffered serious reputational” harm when named in a former British spy’s 2016 dossier about alleged links between Donald Trump and Russia, lawyers have told a judge.

Lawyers representing Aleksej Gubarev, who has sued Christopher Steele, told Mr Justice Warby that part of the “Steele Dossier” named the businessman.

They said one memorandum made “grave” allegations “as to knowing involvement” in the hacking of the computer systems of the United States Democratic National Committee in the run-up to the 2016 US presidential election.

Mr Steele is fighting the case.

The judge began overseeing a High Court trial in London on Monday.

He is expected to consider evidence and argument over five days.

Mr Gubarev took legal action after BuzzFeed published the “Steele dossier” in January 2017, the month Mr Trump was inaugurated as President of the United States.

Andrew Caldecott QC, who leads Mr Gubarev’s legal team, said the case centred on one memorandum from the dossier.

“The dossier consisted of memoranda,” he told Mr Justice Warby, in a written case outline.

“Seventeen were published to the world at large by BuzzFeed on January 10 2017, when Mr Trump was president-elect but not yet inaugurated.

“The general subject matter of the memoranda was the relationship between Mr Trump, his campaign team and Russia.

“The publication predictably attracted enormous publicity both online and in the mainstream media.”

He said one memoranda named Mr Gubarev and made “grave allegations as to knowing involvement in the hacking of the computer systems of the United States Democratic National Committee in the run-up to the 2016 US presidential election”.

Mr Caldecott said Mr Gubarev had suffered “serious reputational harm”.

Detail of the case emerged at a preliminary hearing earlier this year.

Lawyers representing Mr Gubarev then described the dossier as a “notorious document”.

Mr Caldecott said the dossier had been commissioned by a company acting for a law firm.

But he said the “ultimate client” had been the “Democratic National Committee and/or Hillary Clinton’s presidential election campaign”.