So he chose to claim ignorance, in the hope that he can ride this out. It is to be his last line of defence, as all the others crumble before him.

Determinedly, the truth has marched past the Schrodinger’s party defence, in which an event may or may not have happened, depending upon Sue Gray’s observation of it. 

Forthrightly, it has breached the second line, in which Mr Johnson did not know about any event that may or may not have happened.

Heroically, it has ploughed through the third line, in which the Prime Minister was assured that any event that might have happened must have been within the rules. 

And at last, it has reached the castle keep – Mr Johnson’s own private thoughts – where it is revealed that he did indeed observe an unknowable event, but did not know what it was he saw.

And though this may hold the police at bay, it cannot obscure the bleeding obvious from everyone else.