Jeremy Corbyn is now in charge – even though he isn’t prime minister.

And he faces the most important judgement of his life in the coming days.

Does he allow a general election before the EU council of 17 October and take the risk of Johnson winning that election and repealing the law (likely to be passed in coming days) that would force him to ask for a Brexit delay?

Or does he keep Johnson dangling, because with the support of the 21 Tory MPs expelled last night by Johnson, Corbyn now has the power to decide when and even whether there is a general election?

He could insist that no election will be permitted till Johnson has attempted what the PM insists is eminently possible (don’t snort, David Gauke), namely negotiating with the EU those famously elusive alternative arrangements that would see the backstop removed from May’s Brexit deal.

Corbyn will be aware that the spectacle of Johnson begging EU leaders for a Brexit deal would see Johnson humiliated and the Tory party losing yet more support to the Brexit party.

There would be costs to Labour from keeping Johnson dangling, because both main parties have suffered ebbing support for their respective failures to either deliver Brexit or revoke it.

But the costs to the Tories would be worse.

Here is the measure of the madness. Johnson doesn’t have the numbers to do anything, yet it may not be in Corbyn’s and Labour’s interest to put him and us out of our misery.

This is not a constitution crisis. It is a constitutional failure.

Robert Peston is ITV’s Political Editor. This article originally appeared on his ITV news blog.