Chris Mason: Another crunch moment for Starmer as he pleads with Labour MPs not to topple him

Incidentally, don’t underestimate what a big deal it is for any individual MP to go over the top and say their boss should go – not least because, for now at least, those that have done so are a tiny fraction of the total number of Labour MPs.

And it was his name up in lights as their leader when many of them won their seats for the first time, and often in parts of the country where Labour rarely if ever win. So to say now, out loud, that you think he is a dud is a big deal.

Wherever you look in the Labour Party right now there are knots of anxiety.

Firstly, there is anxiety in Downing Street, of course. They are acutely aware of what is at stake.

Secondly, there is anxiety among the potential challengers, weighing up if, when or whether to go for it. Timing can be everything: get it right, and the premiership can be yours. Get it wrong, and what might be your only chance to be prime minister is gone.

Thirdly, there is anxiety among the many, many Labour MPs keeping their heads down and who really don’t want the prime minister to leave right now, nor for there to be a leadership contest.

Then there are those who would like Mayor of Greater Manchester Andy Burnham to be Labour’s next leader and so don’t want a contest right now – because he needs time to firstly find and then win a Westminster seat, having been blocked from standing in one just a few months ago.