https://www.bbc.co.uk/news/uk-politics-53215531


There have been no secrets about the government's ambition to shake up how it does business.

And there has never been any mystery about the desire of the prime minister's top adviser, Dominic Cummings to change Whitehall. What might, perhaps have been rather abstract and hypothetical is becoming real.

Because it doesn't just matter who the politicians are that set the direction of the government. It's not just important who their unelected advisers are, who suggest, cajole and promote their ideas.

But the officials who are charged with carrying out their agendas are crucial, too.

While politicians and governments come and go, the civil service is a constant, impartial organisation that is there to make elected administrations' plans happen, but there to provide advice and stability, too.

The departure of Sir Mark Sedwill matters therefore - the cabinet secretary is the boss of thousands and thousands of civil service, and holds the ultimate responsibility for making the government machine work.

And he is the third senior official to have called it quits on Boris Johnson's government.