For what it is worth, I think it crazy for Labour to decline to take part in a unity government. It need only be one lasting a few days, sufficient to put legislation in place for an extension, and then to call a general election. Refusing to do so does, in the words of Rebecca Long-Bailey "give Boris some sort of get out of jail free card."

Reading more closely, though, the argument is not as much about whether there could be a unity government as about who leads it. Again, that would be a stupid thing over which to wreck the idea.