The second memo was written by Cody Shearer, a controversial political activist and former journalist who was close to the Clinton White House in the 1990s.

Unlike Steele, Shearer does not have a background in espionage, and his memo was initially viewed with scepticism, not least because he had shared it with select media organisations before the election.

However, the Guardian has been told the FBI investigation is still assessing details in the ‘Shearer memo’ and is pursuing intriguing leads.

One source with knowledge of the inquiry said the fact the FBI was still working on it suggested investigators had taken an aspect of it seriously.