The allegations that have surfaced are the most explosive yet about Donald Trump and the Kremlin. A spicy tale of sex and money, clandestine meeting, blackmail and cyber warfare laying bare, it is claimed, how the “Muscovian candidate” was put into the White House in a plot of extraordinary reach.

The 35 pages of supposed revelations have, unsurprisingly, led to bitter accusations and recriminations. Mr Trump has accused America’s intelligence agencies of “one last shot” of sabotaging his presidency. “Are we living in Nazi Germany?” He demanded to know. “Russia has never tried to use leverage over me. I HAVE NOTHING TO DO WITH RUSSIA – NO DEALS, NO LOANS, NO NOTHING!”, he said in one of his many Twitter posts, his favourite form of communications, in a few hours.

These are not refutations of specific charges made in the dossier, although that may come later. The President-elect has also taken more than a week to respond after, if numerous senior security sources are to be believed, receiving them the same time as President Obama. His spokeswoman Kellyanne Conway said Mr Trump was “not aware” that the material was included in a report he had received.

In another tweet, Mr Trump wanted to stress: “Russia just said the unverified report paid for by political opponents is ‘A COMPLETE AND TOTAL FABRICATION, UTTER NONSENSE’. Very unfair! Dmitry Peskov, Vladimir Putin’s spokesman, called the claims “pulp fiction”. He added: “This is an absolute canard, an absolute fabrication, and it’s complete nonsense: The Kremlin does not engage in collecting Kompromat.” Mr Peskov was being somewhat economical with the truth when it came to that statement. All intelligence services with the resources – Russian, American, British – are avid collectors of Kompromat, the Russian acronym for compromising material used in the espionage world.

As in so much else in that world, it is not easy to navigate between truths, secrets and lies: in the words of James Jesus Angleton, a former CIA senior official of renown, intelligence officials often finding themselves in “a wilderness of mirrors”.

What we do know about the allegations is that they contain claims that can be challenged, but, in the view of American and British officials, the document is not a hoax. The British connection is of some relevance here; much of the material, it appears, was put together by a former senior British intelligence official.

The official’s work had involved the former Soviet Union and Warsaw Pact countries during the Cold War and he had maintained contacts since in Russia and eastern Europe while working as a security consultant. Importantly, he is well known to the American agencies and, according to senior sources, they felt the official had enough credibility to be taken seriously.

One matter that appear to buttress this credibility was a report he supplied five months ago claiming that figures in Mr Trump’s campaign team had agreed to a Russian request to try and dilute election focus on its intervention in Ukraine. Four days later Mr Trump stated that he would recognise Moscow’s annexation of Crimea. A month later officials involved in his campaign asked the Republican Party’s election platform to remove a pledge for military assistance to the Ukrainian government against separatist rebels in the east of the country.

The former official had claimed that the Trump campaign acted the way it did before it was aware that the Russians were hacking Democratic Party emails. No evidence of this has been made public, but the same day that Mr Trump spoke about Crimea he called on the Kremlin to hack Hillary Clinton’s emails.

A month before the July report the former intelligence official claimed that the Kremlin had been cultivating Mr Trump for five years and had offered him real estate deals in developments, particularly in relation to the 2018 World Cup finals. At that time he also made the claim that the Russian intelligence service, the FSB, had videos and recordings of Mr Trump in a Moscow hotel with prostitutes – material that could be used to carry out blackmail.

A significant portion of the information that was passed to the FBI came from Senator John McCain. The chair of the Senate Armed Services Committee, with extensive intelligence contacts, is said to have been impressed by the source of the information. But today the Senator said he had sent the information to James Comey, the FBI director, because he was “unable to make a judgement about accuracy”.

There are details in the “dossier” that appear to be mistakes and have been denied. There are misspelling of names of Russian banks and positions of Russian officials. Crucially, it described a meeting between Michael Cohen, a lawyer acting for Mr Trump and a Russian official in Prague. Mr Cohen claimed that he had never been to Prague and tweeted a copy of his passport.

Current and former security officials suggested that possible mistakes and discrepancies may be due to the material being “raw intelligence” that had not been thoroughly vetted. Patrick Skinner, a former CIA analyst, commented: “I imagine a lot more will come out, much of it will be nothing and perhaps some of it will be meaningful and perhaps even devastating.”