Britain's Ambassador to Washington has described Donald Trump as "inept", "insecure" and "incompetent" in a series of explosive memos to Downing Street.
Sir Kim Darroch, one of Britain's top diplomats, used secret cables and briefing notes to impugn Trump's character, warning London that the White House was "uniquely dysfunctional" and that the President's career could end in "disgrace".
His bombshell comments risk angering the notoriously thin-skinned President and undermining the UK's "special relationship" with America.
In the memos, seen by The Mail on Sunday following an unprecedented leak, Sir Kim:
• Describes bitter conflicts within Trump's White House – verified by his own sources – as "knife fights";
• Warns that Trump could have been indebted to "dodgy Russians";
• Claims the President's economic policies could wreck the world trade system;
• Says the scandal-hit Presidency could "crash and burn" and that "we could be at the beginning of a downward spiral... that leads to disgrace and downfall";
• Voices fears that Trump could still attack Iran.
In one of the most sensitive documents, Sir Kim writes: "We don't really believe this Administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept."
He also says that he doesn't think Trump's White House will "ever look competent".
In reference to Trump's ability to shrug off controversies in a life which has been "mired in scandal", he says that the President may nonetheless "emerge from the flames, battered but intact, like [Arnold] Schwarzenegger in the final scenes of The Terminator".
He warns senior politicians in London: "Do not write him off."
The leak is embarrassingly timed for the British Government, coming just weeks after the Queen welcomed Trump and his family with a 41-gun salute and a State banquet at Buckingham Palace as part of a diplomatic drive to secure a post-Brexit free-trade deal.
In a memo sent after the visit, Sir Kim warned that while Trump and his team had been "dazzled" by the visit, and the UK might be "flavour of the month", Trump's White House remained self-interested: "This is still the land of America First".
The Washington Files span the period from 2017 to the present, covering everything from Trump's policy in the Middle East to his 2020 re-election plans.
One account of a Trump rally says that there is a "credible path" for Trump to win a second term in the White House – but describes the crowd as "almost exclusively white".
In what is likely to be regarded as a patronising passage in the cache, officials in London are told that in order to deal with Trump effectively "you need to make your points simple, even blunt".
The most incendiary paper is a letter to National Security Adviser Sir Mark Sedwill sent on June 22, 2017 – 150 days into the Trump administration – and copied to what Sir Kim describes as a "strictly limited" number of senior figures in Downing Street and the Foreign Office.
The document, sent ahead of a National Security Council discussion on the UK-US relationship, paints a damning picture of the President's personality and leadership style.
It says media reports of "vicious infighting and chaos" inside the White House – dismissed by Trump as "fake news" – are "mostly true".
And referring to allegations of collusion between the Trump camp and Russia – since largely disproved – the memo says: "The worst cannot be ruled out."
The cache also includes diplomatic telegrams – known as "DipTel" in Foreign Office jargon – updating Downing Street on political events in the US and providing commentary on Trump's foreign policy decisions.
They reveal details of highly sensitive negotiations over efforts to curb Iran's nuclear weapons programme, as well as the disarray surrounding the President's handling of recent attacks on oil tankers in the Strait of Hormuz.
One memo, sent by Sir Kim on June 22, refers to "incoherent, chaotic" US-Iran policy, adding: "Its unlikely that US policy on Iran is going to become more coherent any time soon. This is a divided Administration".
He questioned Trump's recent claim that he aborted a missile strike on Iran because it would have caused a predicted 150 casualties, saying it "doesn't stand up".
"It's more likely that he was never fully on board and that he was worried about how this apparent reversal of his 2016 campaign promises would look come 2020" – at the next Presidential election.
Another memo, sent on June 10, warns of tensions ahead over Brexit: "As we advance our agenda of deepening and strengthening trading arrangements, divergences of approach on climate change, media freedoms and the death penalty may come to the fore."
The leak of diplomatic cables is extremely unusual and will raise new questions about morale in the Civil Service.
There is mounting evidence that Brexit has politicised many mandarins, with officials who privately support Brexit accusing the Civil Service of trying to stop the UK leaving the EU.
Darroch, who became British Ambassador to Washington in January 2016, is a former UK Permanent Representative to the EU and widely regarded as a europhile.
The Foreign Office last night said that the British public "would expect our Ambassadors to provide Ministers with an honest, unvarnished assessment of the politics in their countries".
A spokesman added: "Their views are not necessarily the views of Ministers or indeed the Government. But we pay them to be candid, just as the US Ambassador here will send back his reading of Westminster politics and personalities.
"Of course we would expect such advice to be handled by Ministers and civil servants in the right way and it's important that our Ambassadors can offer their advice and for it remain confidential.
"Our team in Washington have strong relations with the White House and no doubt that these will withstand such mischievous behaviour."