Donald Trump dossier: intelligence sources vouch for author's credibility

The former Foreign Office official, who has known Steele for 25 years and considers him a friend, said: “The idea his work is fake or a cowboy operation is false – completely untrue. Chris is an experienced and highly regarded professional. He’s not the sort of person who will simply pass on gossip.”

The official added: “If he puts something in a report, he believes there’s sufficient credibility in it for it to be worth considering. Chris is a very straight guy. He could not have survived in the job he was in if he had been prone to flights of fancy or doing things in an ill-considered way.”

That is the way the CIA and the FBI, not to mention the British government, regarded him, too. It’s not hard to see why.

A Cambridge graduate, Steele was one of the more eminent Russia specialists for the Secret Intelligence Service (MI6). The Guardian understands that he focused on Soviet affairs after joining the agency, and spent two years living in Moscow in the early 1990s.

This was a period when Russia and the breakup of the eastern bloc were still the prime focus for Britain’s intelligence agencies, and a successful spell in the region was a good way to get on.

By all accounts, that’s exactly what Steele did. And his interest in Russia did not diminish as he continued to rise up the ranks, a friend and contemporary of Alex Younger – now head of MI6.

Over a career that spanned more than 20 years, Steele performed a series of roles, but always appeared to be drawn back to Russia; he was, sources say, head of MI6’s Russia desk. When the agency was plunged into panic over the poisoning of its agent Alexander Litvinenko in 2006, the then chief, Sir John Scarlett, needed a trusted senior officer to plot a way through the minefield ahead – so he turned to Steele. It was Steele, sources say, who correctly and quickly realised that Litvinenko’s death was a Russian state “hit”.