What does that mean?
MI6 knows what happened and is suggesting the Saudis must fix their problem. It is a well-known thing that MI6 has a vast reach in the Middle East. So it will have knowledge of the facts. It is letting the Saudis know via the ex-head.
But they don't want to be seen taking the Saudis on in a way that the leaders of SA will lose face.
That's how you do it using soft power. I think MBS will be steered out of government.