The resignation of Sir Kim Darroch followed the failure of the probable next prime minister, Boris Johnson, to say he supported him staying in post, despite being given repeated chances to do so during his TV debate on Tuesday night with Jeremy Hunt. As the current Foreign Office minister Alan Duncan put it, by six times refusing to back the ambassador, Johnson had thrown him under a bus.

Without the backing of the US president or his future boss, Darroch naturally concluded he had no future as an interlocutor between London and Washington. He realised, in the words of a friend who spoke to the Guardian, that Johnson had left him no option.

There is now shock and contempt across the Foreign Office and in parliament, not just towards the leaker and Trump but also towards Johnson. Whatever sanctimonious expressions of regret Johnson mouths and however much he blames the leaker, the Foreign Office knows he effectively sacked Darroch, believing he was carrying out the orders of Donald Trump

 

His resignation means the malicious leaker has got his or her way. It was pretty clear from the outset that the political purpose of the leak was to get Darroch removed, to be replaced by a true Brexiter of the kind that Nigel Farage – and now, apparently, Johnson – believes is necessary if the UK is to extract maximum political and economic value from Brexit.

It was also clear that despite the Foreign Office’s protestations, Trump was determined to blackball Darroch. The ambassador excluded himself from a meeting between the trade secretary, Liam Fox, and Ivanka Trump to avoid any embarrassment for the president’s daughter. But he found himself struck off the dinner guestlist for the visit of the emir of Qatar, and a second meeting between Fox and Wilbur Ross, the US trade secretary, did not go ahead.

Darroch spent a restless night pondering whether to quit or try to soldier on until he was due to retire at the end of the year. When he was reached on the phone early on Wednesday morning by Sir Simon McDonald, the permanent secretary at the Foreign Office, it was clear to McDonald that the ambassador had made up his mind. According to McDonald, Darroch felt that as long as he stayed in Washington he and his family would be a target.

An ambassador can acquire a personal profile but they should not become the story or see their views unmoored from the government they represent. Darroch could sense that a wounded Trump meant to carry out the threat to ostracise him. A diplomat is by profession the ultimate networker and cannot continue if the lines of communication are cut.

These were all cogent reasons to resign. Johnson’s decision not to defend him was a deliberate act of sabotage. His explanation that if he had defended him he would have unfairly dragged Darroch into politics was bogus.

Johnson chose to betray him because he regards his relationship with Trump as critical to the success of Brexit, and he simply could not afford to to start his premiership with a standoff with the US over an emissary for whom he anyway had little sympathy.

Barring a daring pre-emptive appointment by May designed to thwart Johnson, the chances now rise that an external political appointment of the kind advocated by Farage will be made. It would not be unprecedented. But the loss of Washington to, for instance, a Brexit businessman would be a blow to the prestige of the diplomatic service and represent a further sign that in these riven times the concept of a neutral civil service is harder to protect. Diplomatic telegrams in future will all be a bit more grey and circulated to fewer pairs of eyes.

Those populist Brexiteers that blame the disappointments in their cause on treacherous civil servants will feel they have claimed a scalp. But the episode possibly foretells something about the nature of the special relationship under Trump and Johnson. The former foreign secretary David Miliband, for example, said Johnson’s eagerness to please the White House signalled a weakness inherent in the Brexit process. “In today’s global village, when you pull away from your neighbours everyone can take advantage,” Miliband said.

By putting all his chips on Trump and going for the kind of hard Brexit the president believes is available, Johnson clearly hopes he will get a generous and quick free-trade deal with the US. Political goodwill is the key to unlocking this.

The last three days have shown a man who when asked to jump only answers: “How high?” It is not surprising that the Trump administration is so optimistic that Johnson will follow Trump’s thinking on issues such as Iran, Huwaei and Israel.

The incident has also told the civil service about Johnson as a man. For some he will have revealed himself to be shallow and willing to take advantage of an illegal leak to oust a civil servant who had dedicated himself to public life. Yes, ultimately the leaker is to blame, and Trump’s thin skin, but evasion of personal responsibility is already becoming the defining negative feature of Johnson’s candidacy.

When he goes through the doors of No 10 at some point this month, smiling and wanting to be loved, many will instead see only “the nasty piece of work”, as he was described by the broadcaster Eddie Mair.

In the words of the chair of the foreign affairs select committee, Tom Tugendhat, a former army officer: “Leaders stand up for their men. They encourage them to try and defend them when they fail.”

There is now shock and contempt across the Foreign Office and in parliament, not just towards the leaker and Trump but also towards Johnson. Whatever sanctimonious expressions of regret Johnson mouths and however much he blames the leaker, the Foreign Office knows he effectively sacked Darroch, believing he was carrying out the orders of Donald Trump.