AND THE OTHER 20% IS TOO DELICIOUS NOT TO SHARE:

One of the reasons his dossier was taken seriously in Washington in 2016 was Steele's reputation in the US for producing reliable reports on Russia, according to Harding's book.

Between 2014 and 2016, he authored more than a hundred reports on Russia and Ukraine, which were commissioned by private clients but shared widely within the state department and passed across the desks of the secretary of state, John Kerry, and the assistant secretary Victoria Nuland, who led the US response to the annexation of Crimea and the covert invasion of eastern Ukraine.

The sources for those reports were the same as those quoted in the dossier on Trump, which included allegations that the Kremlin had personally compromising material on the US president, including sex tapes recorded during a trip to Moscow in 2013, and that Trump and his associates actively colluded with Russian intelligence to influence the election in his favour.

Years earlier, Steele shared the results of his investigation of the global football organisation, Fifa, with a senior FBI official in Rome; that led to an investigation by US federal prosecutors, and ultimately the arrest of seven Fifa officials.

"The episode burnished Steele's reputation inside the US intelligence community and the FBI. Here was a pro, a well-connected Brit, who understood Russian espionage and its subterranean tricks. Steele was regarded as credible," Harding writes.

The book traces Steele's career as an MI6 officer, sent to Moscow in 1990 under cover of working as the second secretary in the UK chancery division at the embassy.

While there, the young spy was witness to the 1991 attempted coup and looked on when Boris Yeltsin climbed on a tank in central Moscow to denounce the plotters.

Steele left Moscow in 1993 and was later posted to Paris before taking a senior post on MI6's Russia desk in London in 2006. Because his name had been on a list of MI6 officers leaked and published in 1999, he was unable to return to Moscow. But he was chosen to lead the MI6 investigation of the assassination of the former FSB officer Alexander Litvinenko by radioactive poisoning in 2006.

Steele left MI6 in 2009, to start up a commercial intelligence firm, Orbis, with a former colleague, Christopher Burrows. Soon after its founding, Orbis began working with Fusion GPS, a Washington-based company doing political and business research, which commissioned the investigation of Trump in 2016.

Steele delivered a total of 16 reports to Fusion between June and early November 2016, but his sources started to go quiet beginning in July, when Trump's ties to Russia came under scrutiny. According to Harding's account, Steele was shocked by the extent of collusion his sources were reporting.

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