If Cameron fails in his "passionate" determination to preserve the Union, he gets a consolation prize: a generation of Tory governments in England. Ed Miliband's consensual commitment to the Union has a little self-interest in it: a swag of Scottish Labour MPs.
The other advantage for the poor fellow is that he can avoid being dragged round the chamber by his shirt collar because he's agreeing with the PM for once. Things are collapsing rapidly for the Labour leader. Last year, he got a big cheer from the PLP when he roundly declared he could beat David Cameron at the despatch box. The bigger cheer came yesterday when the Tories welcomed him to the despatch box with noisy – but ambiguous – approval. They now see what a strategic asset Ed – sweet, decent Ed – is for the Coalition.
He did not disappoint them. He didn't disappoint anyone. He is beyond disappointment. He is now in the zone of morbid curiosity.
He used his weary voice to ask why the Coalition had allowed the train companies to get away with an 11 per cent fare rise. Cameron answered in one sentence ("Because the power to do that had been given by the last government") and sat down.
At a critical moment, Ed might have scored by leaving his script and making Cameron answer the question: "If he thought our policy was so bad, why did he reinstate it?" He lost the exchange in the chamber with a plaintive delivery that said: "Why won't he listen to me, he's just not taking me seriously?"
Afterwards, it looked like he lost the argument on the franchise agreement as well (the Labour fare cap expired automatically, it was not overturned by the Coalition).
When the history of Ed's decline and fall is written, this will be a page in it. The one thing a policy wonk needs is a command of the detail. Indeed, his previous theme had been to crow at the PM: "He doesn't know the detail of his own legislation." Here Ed didn't know the detail of his own question.
Everyone says it is too difficult to unseat a Labour leader. A stalking horse would be a start. A suicidal mission, but honourable. We all remember the name of Sir Anthony Meyer. And those who don't can Google the man who brought down Mrs T.