“The president fundamentally wants to be liked,” says Katie Walsh, former White House deputy chief of staff, in Michael Wolff’s book Fire and Fury. “He just fundamentally needs to be liked so badly that it’s always …everything is a struggle for him.”

The world’s greatest egos are often the most frangible. According to a source close to Donald Trump quoted in the Sunday Times, he cancelled next month’s presidential visit to the UK because he felt he had “not been shown enough love” by Theresa May’s government. Naturally, the snowflake-in-chief needed a pretext for calling off the trip – though his official excuse was hilariously flimsy. “I am not a big fan of the Obama administration having sold perhaps the best located and finest embassy in London for ‘peanuts’,” he tweeted last week. “Bad deal. Wanted me to cut ribbon – NO!” Meanwhile, in an intervention that would have seemed astonishing under almost any other administration, Woody Johnson, the US ambassador, immediately contradicted his boss in the London Evening Standard, declaring that “the new embassy is not just bigger, it is better and capable of meeting the complex challenges of the 21st century and beyond”.

In any case, it is transparently obvious that Trump’s cancellation was driven by smouldering pique rather than his supposed outrage at the embassy’s move from Grosvenor Square in Mayfair to the new site near Battersea power station. As Sadiq Khan, London’s mayor, observed, the president seems to have “got the message” that he is not welcome here.

Enter Boris Johnson to reframe the diplomatic debacle with considerable imagination as a dastardly Labour plot. “The US is the biggest single investor in the UK – yet Khan & Corbyn seem determined to put this crucial relationship at risk,” tweeted the foreign secretary. “We will not allow US-UK relations to be endangered by some puffed up pompous popinjay in City Hall.” This was the first prominent outing for that particular word that I’m aware of since George Galloway called the late Christopher Hitchens “a drink-soaked former Trotskyist popinjay” in 2005. It was also a distraction from the real reasons for Trump’s cancellation, of which there are more than 1.8m – the number of signatures on the petition to prevent the president’s state visit that was discussed in parliament last February. Trump is an entertainer before he is a politician. Indeed, he has described himself as a “ratings machine” – which is why he was so furious that his inauguration a year ago was more sparsely attended than Barack Obama’s in 2009. It must be intolerable to this bigoted ham that his dreadful act is simply not wanted in a global city such as London.

Which brings us to the notion of “narcissistic supply”, first coined by the psychoanalyst Otto Fenichel in 1938 to describe a narcissistic dependence on adulation and admiration. Trump’s view of the “special relationship” has begun to resemble this addictive emotional disorder.

The foreign secretary is under no illusions about the president’s true nature. In December 2015, when still mayor, he reacted angrily to his allegations about Islamist radicalisation in London, insisting that: “The only reason I wouldn’t go to some parts of New York is the real risk of meeting Donald Trump.” Since the presidential election, however, Johnson has broken bad, cooking up the crystal meth of approval that Trump so badly needs. In July, he praised the president for gripping “the imagination of people around the world”. In November, he celebrated Trump as “one of the great huge global brands”.

What does it say about Britain, and our sense of national self-worth, that we indulge such a man?

Initially, No 10 was not sure last week whether the foreign secretary was speaking for the government in his attack on Khan and Jeremy Corbyn, before eventually conceding that he was – which is a constitutional relief – but it entered the caveat that “Boris expresses himself in his own inimitable way”.

There is something truly wretched about this government’s continued appeasement of a president who has strained every notion of decency and international propriety. So desperate are senior ministers not to jeopardise the “very big and exciting” trade deal promised to them by Trump that they lurk, shamefully, at the fringes of complicity in his worldview, praying that he will cut them a break. This they do, in spite of all the evidence that he has no such intention. As Sir Nigel Sheinwald, the former British ambassador to the US, puts it, all hopes of a swift transatlantic compact should now be “put out of our minds”.

Such are the bleak wages of Brexit, the ashen taste of diminishing global power. This is a president who has repeatedly scorned our response to Islamist terrorism, retweeted anti-Muslim videos posted by the deputy leader of the ultranationalist group Britain First, and needled the mayor of our capital for sport. In August, after the violent white nationalist rally in Charlottesville, Virginia, he failed the most basic test of geopolitical leadership, declining to sign up unambiguously to the proposition that neo-Nazis are uniquely bad. Last week, he reinforced that failure, describing Haiti, El Salvador and certain African nations as “shithole countries”.

What does it say about Britain, and our sense of national self-worth, that we indulge such a man? I do believe that there is what Barack Obama called a “partnership of the heart” between Britain and the US. I also believe that the principles enshrined in this historic relationship are too precious to be sacrificed on the altar of Trump’s epic narcissism. To stand a chance of recovery, an addict must first admit he has a problem. This president won’t, which is why – now more than ever – the US needs honesty from its real allies. The least we can do is to stop enabling him.

• Matthew d’Ancona is a Guardian columnist