One of Boris Johnson’s closest allies, David Frost - who has been negotiating the terms of the UK’s future relationship with the EU - is to become National Security Adviser, in succession to Sir Mark Sedwill, who is standing down both as cabinet secretary and NSA.

This is an unusual and controversial appointment because Frost is a political appointment, a special adviser, in his current role - and will continue as a political adviser rather than becoming a member of the civil service.

There will be a formal process to find a new cabinet secretary.

Frost is close to Dominic Cummings, and is routinely referred to as "Frosty" in Johnson’s circle.

So anyone who has persuaded themselves that Cummings's influence has waned may need to re-think.

Cummings's pervasive influence was also manifest in the Ditchley Lecture given by Michael Gove, which contained more details on Cummings’s long-standing plan to end alleged Whitehall groupthink by replacing traditional mandarins with data scientists and physicists (or at least supplementing the humanities crowd with those from "harder" disciplines).

But back to Frost - whose appointment is bound to cause a bit of a big gulp among the spooks and military top brass. "They are not happy," said one military source.

Johnson is generous to Sedwill in a handwritten letter to him, thanking him for being a bridge to the new order of things since he became PM 11 months ago.

And Sedwill will have an enduring role on the UK’s behalf, chairing the panel on global economic security when the UK assumes the presidency of the G7 group of leading industrial nations next year (which seems an odd appointment, given that Sedwill’s expertise is in the world of spooks not economics).

But there has been gossip in Whitehall for months that he was not performing the central role expected of cabinet secretaries.

One cabinet member said that since Simon Case was appointed to the new role of 10 Downing Street's permanent secretary "Mark has been invisible".

One important question - that will be answered by an expected future public inquiry - is what kind of role Sedwill has played in the coronavirus disaster.

Senior Whitehall figures have complained he has not gripped the crisis to the extent they would have expected.

However, the PM in his letter praised Sir Mark’s work on limiting the damage of the Covid-19 epidemic and in helping to deliver Brexit.

In Sir Mark’s letter to the PM he acknowledges that his dual role as cabinet secretary - the most senior member of the home civil service - and national security adviser was exceptional.