In the end Gordon Brown knew he had to move. By this morning 46 Labour Mps had signed up to an amendment that would have suspended the abolition of the 10p rate of tax until new measures came forward. He was heading for defeat next Monday on that amendment unless he put flesh on the bones of promises earlier this week to come forward with compensating measures in the autumn.

So Alistair Darling used a tried and tested device - a letter to the chairman of the Treasury Select Committee setting out his thoughts for the future. Mr Brown and Mr Darling had lengthy meetings over recent hours to finalise the package. In the letter Mr Darling promised to look specificially at the case of particular groups, pensioners aged beteen 60 and 64, and low-paid workers without children. Crucially he gave the rebels what they wanted - any change would be backdated to the start of this financial year.

The rebels, most of whom did not want to vote against the Government next week, chose to declare "game set and match" and withdrew their amendment even though they would be the first to admit that there remain many questions over what Mr Darling will eventually do and what it will cost. The immediate peril to Mr Brown's leadership is over, but at what cost?

For David Cameron there was little other to do than to attack Mr Brown for his dithering and his "humiliating" climbdown. Mr Brown, he said, had only acted because he knew he was going to lose next week, not for any other reason.

In truth the Tory fox has been shot and the Prime MInister decided to kill it because it was doing him and his party untold harm in the run-up to next week's London mayoral and local elections.

But what does this mean for the future? It shows Labour MPs that they can get their way if they shout loud enough. Mr Brown succumbed, mainly to the press, over capital gains tax and non-doms. But here, he gave in to his party because it was telling him it did not like what he had done.

Will those same MPs now scent that when it comes to rebellions Mr Brown can be a bit of a pushover? Will this not embolden the much larger group of MPs opposed to his plan to hold terrorist suspects for 42 days to carry on their revolt, even if it means an embarrassing defeat for Mr Brown in June?

Those are questions which will haunt the Labour whips in the weeks and months to come. But this lunchtime they are a mightily relieved bunch. They knew that without concessions they could not have delivered next Monday's vote for Mr Brown.

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