A British former spy who wrote a 2016 dossier about alleged links between Donald Trump and Russia has told a judge he did not foresee a media organisation obtaining copies.

Christopher Steele told Mr Justice Warby he took great care to ensure intelligence was handled and communicated carefully.

Mr Steele said his business depended on confidentiality, and told the judge he never “knew, intended or foresaw” that any media organisation would publish information from the dossier to the “world at large”.

He was giving evidence at a High Court trial in London on Wednesday after being sued for defamation by a Russian businessman named in the dossier.

It would be professionally ruinous – and also morally repugnant – for us to do anything that could risk exposing a source

Aleksej Gubarev, who runs an IT infrastructure business, has told the judge he was stunned when BuzzFeed reported that the Steele dossier had linked him to a US Democratic Party “hacking incident”.

Mr Gubarev, and a company he runs called Webzilla, took legal action after BuzzFeed published the dossier in January 2017, the month Mr Trump was inaugurated as president of the United States.

He says he has been defamed by Mr Steele and Orbis Business Intelligence, a London-based corporate consultancy co-founded by Mr Steele, and wants “very substantial” damages.

Orbis and Mr Steele are fighting the claim and deny defamation.

“It is not in Orbis’s interest for any of our intelligence work to be aired in the media or public domain, especially in raw or unanalysed form,” Mr Steele told the judge, in a written witness statement.

“Our business depends on the confidentiality of our clients and sources. If these are exposed to the world, no-one will contact Orbis to do discreet work on their behalf.

“It would therefore be professionally ruinous – and also morally repugnant – for us to do anything that could risk exposing a source, especially in a ruthless, lawless place like Russia, as a result of any such (especially media) exposure.”

He said that if he had known that BuzzFeed had a copy of the dossier, and intended to publish, he would done “whatever I could do to prevent this”.

The dossier was commissioned by a Washington consultancy acting for a law firm, the judge has heard.

He has been told that the “ultimate client” was the “Democratic National Committee and/or Hillary Clinton’s presidential election campaign”.

Lawyers representing Mr Gubarev have said there is no suggestion the allegations against Mr Gubarev and Webzilla were true.

They say BuzzFeed apologised and redacted the names of Mr Gubarev and Webzilla from its website.

The lawyers said Mr Gubarev is not suggesting Orbis and Mr Steele had been “malicious”, but the central question is whether they were “responsible in law” for the publication of the dossier by BuzzFeed.

Mr Gubarev’s case is that they were.

Mr Steele disagrees and says the claim should be dismissed.