Hall Hall, a 33-year veteran of the UK foreign service, and a former ambassador to Georgia, said UK institutions had been undermined and the reputation of British democracy abroad had been imperiled.

“I have been increasingly dismayed by the way in which our political leaders have tried to deliver Brexit, with reluctance to address honestly, even with our own citizens, the challenges and trade-offs which Brexit involves; the use of misleading or disingenuous arguments about the implications of the various options before us; and some behaviour towards our institutions, which, were it happening in another country, we would almost certainly as diplomats have received instructions to register our concern,” she wrote in her letter, dated December 3.

“It makes our job to promote democracy and the rule of law that much harder, if we are not seen to be upholding these core values at home.”

Delivering Brexit has been impossible. Stopping it will be even harder

Hall Hall said she could no longer reconcile her commitment to the job with the demands made of her. “I am also at a stage in life where I would prefer to do something more rewarding with my time, than peddle half-truths on behalf of a government I do not trust,” she wrote in the letter.

Though Hall Hall did not refer to Johnson or any other UK leader by name in her letter, she expressed concern about the divisive rhetoric that has characterized British politics since the Brexit referendum.

Johnson’s comments have hardened in recent months. He has attacked attempts to prevent a no-deal Brexit as “surrendering” to Brussels and dismissed fears that his language encourages supporters to abuse his opponents.

Johnson has defended his rhetoric, telling the BBC after a particularly rancorous parliamentary debate in September that avoiding such terms risked “impoverishing the language and diminishing parliamentary debate”.