Donald Trump and Kim Darroch.

The resignation of Sir Kim Darroch proves a few things about the state of the United Kingdom as it edges towards Brexit. Only one is encouraging.

First, Sir Kim’s decision to put country before career shows that there is, in some parts of British life, still such a thing as a sense of honour. After Boris Johnson’s failed to back him in the latest ITV debate he must have realised his position was hopeless; Jeremy Hunt’s robust defence of him is of little use if Hunt doesn’t become PM, as he almost certainly will not.

What, by the way, if it was Johnson who leaked the emails? Although the PM-in-waiting has distanced himself from it. Or leaked them to someone who then leaked them to Isabel Oakeshott, the journalist? The Leave/Brexit Party nexus, pulling in the likes of Nigel Farage and Arron Banks, may be tighter than we imagine.

Ever the professional, with an excellent reputation from all who dealt with him, Sir Kim clearly decided that he was “becoming the story”, and that had made his departure inevitable – because the damage it was doing to Britain’s interests.

Hence his brave move. It is more than regrettable. Donald Trump’s behaviour is beneath contempt. Perhaps the foreign secretary, Jeremy Hunt, can relay that sentiment to the US ambassador to the UK, Robert Woods?

It would be satisfying if Hunt was able to tell him exactly what we think of Trump – wacky and very stupid in fact. Maybe some mysterious clash of diaries meant that Woods’ invitations to Buckingham Palace suddenly were to dry up. For good measure, Mr Hunt could add how much the British people regret ever having that buffoon Trump over for a state visits.

Sir Kim’s humiliation and resignation, by the way, makes it doubly important that the source of the leak is discovered.

The damage is done. Today, what ambassador or high commissioner is not going to hesitate before sending opinions back to London? Now more than ever, electronic communications are prone to hacking and leaks and this high-profile episode will have a chilling effect on the way our diplomats conduct their business.

At a time when the civil service and diplomatic service are increasingly demoralised, suffering a brain drain and being pummelled by political attacks by paranoiac Brexiteers as traitors, Brexit betrayers – Olly Robbins, chief Brexit agitator, being the prime example – we have to resist the politicisation of the civil and foreign services. It is openly talked of now that the cabinet secretary himself, Sir Mark Sedwill, will be pushed out of his job. And look at the carelessness with which secrets about Huawei were tossed out to the nearest hack, apparently by Gavin Williams, the defence secretary himself (although he has denied it).

These are depressing, dangerous developments. There is a huge turnover in the civil service and that is a very unhealthy sign: underpaid, undervalued, under-defended – no wonder they’re clearing off.

The other thing the Darroch affair shows is that the UK is becoming diplomatically exposed and isolated as it moves away from the European Union, with its huge diplomatic and economic clout. “Global Britain” is a bit of a weakling when it can’t even name and retain its own representatives abroad, isn’t it? The debacle of Liam Fox’s aborted trade talks in Washington about sums it up

Who will succeed Sir Kim? You would hope that Hunt and Theresa May would appoint a permanent replacement, a professional who will try and do the job properly before Johnson gets his hands on the shortlisting. If not, then we can look forward to some Farage/Johnson puppet turning up.

So. We’ve lost Sir Kim and a good slice of our national pride. In return we’ll be getting those gold ol’ American chlorinated chickens for dinner, and we’ll have to swallow a lot more besides, like US access to NHS contracts. Great work, Boris.