By John Pienaar
Chief political correspondent, BBC Radio 5 Live
Mr Brown and Mr Darling blinked first
Gordon Brown may be stubborn, but he is not stupid.
"Labour's finally worked out, it has a loser not a leader," David Cameron told him at Prime minister's question time.
That must have stung. But losing next Monday's vote would have hurt far, far more.
So even before the chancellor spelled out the terms of peace, a climbdown seemed inevitable.
As a Fleet Street colleague put it to me early this morning "this Labour rebellion will turn out to be a damp squid".
I think he meant squib, but I liked his version more.
Backbench rebellions, almost always turn out to be wet and rather floppy.
Labour backbenchers have, finally, been given an answer to angry voters on the doorstep as the campaign for the May 1 local elections
Only this time, Gordon Brown and Alistair Darling looked the squid in the eye - the squid stared back - and the prime minister and his chancellor blinked.
By 12pm, minutes after the retreat was spelled out in a letter to the Commons Treasury Committee, David Cameron knew what he had to do.
The Tory leader excels at this kind of mockery. "I think we can call this session Prime Minister's U-turns, rather than Prime Minister's Questions....taking people for fools..."
There was lots more of this, and Conservative MPs lapped it up.
His best lines, though, had been supplied by Labour (former) rebels: "'He's losing touch', 'he doesn't know what fairness is', 'he needs to see the world through the eyes of voters', 'he's like a scared rabbit in the headlights'," recited the Tory leader.
"The Labour peer Lord Desai said your leadership style is like porridge. Another week like this and it will be cheerios." That last gag sounded a bit laboured, but you get the point. He was enjoying himself.
Mr Brown, looking uncomfortable, sounding hoarse, fell back on a recitation of his efforts to fight poverty, dating back to 1997.
Mr Cameron recited Labour MPs' comments
"Here's the choice - a Labour government that supports the minimum wage, supports tackling child poverty and pensioner poverty and has got three million people in jobs; and a Conservative Party that would go for £10bn worth of tax cuts, the priority going to stamp duty on shares and not the poorest in the country."
There was much more of this too. But objectively, this was not a good day for the prime minister. Only a week ago, he appeared to deny anyone was losing as a result of the abolition of the 10p tax band. Now we have a long list of proposed concessions.
Labour backbenchers have, finally, been given an answer to angry voters on the doorstep as the campaign for the May 1 local elections.
The MPs will be grateful. How grateful the angry voters turn out to be remains to be seen. They have been offered an I.O.U but they'll have to wait for their cash.
The pundits say these elections could be tough for Labour, seriously tough if Ken Livingstone happens to lose the London mayoralty to Boris Johnson.
Further rebellions, on the plan for extended detention of terror suspects, for example, still lay in wait.
To be fair, the prime minister's record of trying to fight poverty is well established. The government has averted a defeat on the Finance Bill, a potential disaster.
But U-turns under pressure tend to carry a cost in political authority. Gordon Brown's suggestion that Wednesday's retreat was merely another stage in the project, and his refusal to acknowledge that it was driven by the fear of defeat, were harder to swallow.