Ken as always comments wisely and whilst noting there are differences between the European and US approach to WM's question:
And thirdly: What is the tipping point for resignation as opposed to acquiescence or possibly brown nosing ?
It is quite clear, even for someone not within, that a good number of British Army officers have taken another way out - resignation, often after a tour in operational command. A good number have commented in public, usually in carefully phrased media interviews.

Some I expect have other reasons than the political directions given and the military command's response.