Is today the day Labour died?

Will today be the official day when the Labour Party will be seen to have died - or at least cease to resemble a party that could credibly form a government?

This is not hyberbole.

The point is that an overwhelming majority of Labour MPs will today sign a vote of no confidence in Jeremy Corbyn.

And barring a last-second change of heart, he is saying that he will ignore their pleas for him to quit and will remain in office.

At that juncture, Labour in parliament will have no credibility. How could it have the respect of the rest of us with head and body so thoroughly disconnected?

• Live updates: Labour in turmoil

• More analysis from Robert Peston

• MPs in tears as Corbyn refuses to quit

What will then ensue is a life-and-death struggle between Corbyn and his estranged parliamentary party.

There will be a leadership contest between Corbyn and - probably - either Tom Watson or Angela Eagle (for what it's worth, I think it will be impossible for the rebels to keep Corbyn off the ballot paper).

Who will win?

Well although Corbyn probably isn't as popular with Labour's substantial membership as he was, because some of them blame his lackluster referendum campaign for the Leave victory they hate, the chances are he will have his mandate reaffirmed.

So at that juncture Corbyn would have power but zero authority over Labour's MPs.

And that way lies total political irrelevance.