Loads of detail about the cabinet secretary here and in @cath_haddon thread. Now that Mark Sedwill's departure has been announced here are a few other thoughts... https://twitter.com/cath_haddon/status/1277262009508204544

- in the end, if you're cab sec you need to have the confidence of the PM. That's the basis of your ability to get things done. So while a PM can't "fire" the cab sec, like so much in the UK constitution that is a theoretical rather than actual constraint

- cab secs have different styles, so do PMs – so the job can’t be fully defined (though @ereniemb excellent explainer does as far as poss). Jeremy Heywood’s was to make himself indispensable to PMs which gave him capital to argue with them when he chose to pick a battle

- media love “most powerful person you’ve never heard of”, and the job has huge influence. But more on people, apptmts, how things are done, less on policy. While Jeremy Heywood had more influence on policy than most, even that was a few core areas, and when PM disagreed, PM won

- a pompous point, sorry, but as with Rutnam, Kerslake, MacDonald, Devereux, Scholar… it’s not a good look to litigate someone’s job or their competence in the media

- processes protect – having more of an open process around the formal appointment of the cabinet secretary must be a good thing. Gives assurance around the merit of the appointment, status with colleagues and some protection from other attacks

- there’s always briefing about “bringing in someone from business” – but whoever does the job next MUST know how to run the machine. Even with strong backing from PM and a mandate for reform they’ve got to be able to make it work which almost certainly requires some time in govt

and thread ENDS - for the moment, though this will play out for some time to come!