The controversial dossier served as the pretext for the FBI to start spying on Donald Trump's campaign members. A 2019 probe into the agency's activities didn't rule that is actions were inappropriate, but still criticised the FBI over how it handled FISA surveillance requests.

Former Conservative lawmaker Rupert Allason, also known under his alias, Nigel West, is the author of numerous fiction spy books based on historical research, and has concluded in a 2017 research paper that the so-called Steele Dossier was largely made-up by its author, rather than being based on reliable sources, The Sunday Times reported citing the paper which they obtained. He assembled the report at the request of a Republican law firm after the Steele Dossier had been published by the Buzzfeed media outlet.

The former British lawmaker opined that "there is [...] a strong possibility that all Steele’s material has been fabricated" after studying the former MI6 spy's findings and 11 sources he used to draft them.

"From a professional intelligence perspective, the dossier as a whole is profoundly troubling and cannot be taken at face value", Allason said.

Allason said that he was "frankly stunned" by what he saw in Steele's reports, whom he took for a respected former intelligence officer. He specifically cast doubt on one of the more notorious allegations made by Steele – that the Russian government had a compromising video, dubbed a "pee tape", in order to blackmail Trump.

"The content has such explosive implications that there is an added responsibility on a reporting officer to be entirely unambiguous as to precisely who has said what, and when, while explaining the status of each individual", the former lawmaker noted.

Rupert Allason, who is believed to be an expert in identifying pristine intelligence reports after he wrote an entire book devoted to identifying fake spy stories, reportedly went on to explain that the authors of made-up papers sometimes confuse themselves and attribute information to the wrong source. In the document, cited by the Times, Allason pointed out that Steele attributes too many of his findings about alleged ties between Trump and Russia to a single source, which appears "unprofessional" to the former lawmaker.

"Source E is credited with access to Ritz-Carlton staff, knowledge of Russian government involvement with WikiLeaks and the abuse of Russian diplomatic facilities in the United States. This appears to be an extraordinarily wide area of expertise. The apparent lapses bear the hallmarks of invention", Allason said.

Findings attributed to Source E in Steele's Dossier on Trump paved the road to the FBI's notorious probe, which included espionage on the then presidential candidate's campaign. The FBI later learned that most of information came from a businessman, Sergei Millian (although it's not clear if he was in fact Source E), who claimed that info, which he gave to Steele, was "just talk" one conveys "with friends over beers" and not more than "rumour and speculation" in some cases.

The FBI still failed to notify the FISA court that it considered its own source of information unreliable when it requested the prolongation of surveillance over Carter Page, a member of Trump's campaign team. Such handling of FISA warrants received harsh condemnation from the US justice department’s inspector-general Michael Horowitz, who probed the FBI for misconduct but found no grave violations or bias against Trump in the process.

The Steele Dossier was initially funded by Trump's GOP opponents, but eventually the Democratic National Committee and its candidate in 2016 election, Hillary Clinton, became its main sponsors.