At some point in 2016, a Washington DC based investigative agency began working with a former British foreign intelligence officer to look into Donald Trump's ties with Russia.

Together they compiled a report, purportedly based on testimony from a network of high-placed sources in the Russian government and Mr Trump’s entourage.

Over the summer, the document passed through the hands of senior Democratic party officials, the Republican senator John McCain (who was handed a copy by a former British diplomat who had served in Moscow and passed the document on to the FBI), and several Washington-based journalists.

The Telegraph first heard of some of the allegations in August, when a US former intelligence source said the Russians had material to blackmail Mr Trump. He cited a different source to the former British intelligence officer.

In a press conference on Wednesday, Mr Trump dismissed all of the claims, calling them "nonsense that was released by, maybe the intelligence agencies, who knows, but maybe the intelligence agencies ... It should never have been written, it should never have been released."