Her fellow diplomats have told me that Alexandra Hall Hall was increasingly frustrated with the political talking points she was being given by London on Brexit.
Several weeks ago at a think tank in Washington she was saying privately that she could no longer peddle what she has called the “half truths” of the British government’s Brexit position.
She put it this way in her resignation letter: "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...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."
It’s significance lies in her seniority - she’s a former UK Ambassador - and the fact she was the lead diplomat on Brexit in the USA. I’m told she was having meetings with seasoned American officials in which both sides knew that London’s position was demonstrably false - such as Downing Street’s talk of being able to achieve a quick trade deal with the USA.
All the experts know that it will belong and tortuous. In that sense, Alex Hall Hall’s position had become unsustainable.
The more intriguing question (given that her views are widely shared at British diplomatic missions across the EU and in the US) is whether her resignation will trigger other diplomats and trade officials to quit as well.
Some may follow - either before or after the election next week - though perhaps not with such a withering parting shot at their political masters.