Not for the first time, fallen trade secretary Peter Mandelson has done the best possible thing for the Labour party.

He also set the example for controversial Paymaster General Geoffrey Robinson who had no option but to quit in the wake of Mr Mandelson's resignation.

He had been expected to go as quietly as possible early in the new year, but his decision was hastened by Mr Mandelson's departure.

By resigning over the "loan for a home" row, Mr Mandelson has done everything within his power to draw a line under the government's embarrassment.

And never before has Mr Mandelson found so many admirers across all wings of the Labour party and within opposition parties.

His swift resignation has seen him described as "honourable" and "principled" by people who only a day before would have cast him as some sort of demon and used very different language to portray him.

Even his greatest enemies, who are almost entirely confined to the Labour benches, had to concede he had done the right thing by them.

But there should be no doubt that there was also a huge element of self-interest in the former trade secretary's decision.

If he had held on and been subjected to the kind of concerted attacks some Tory ministers suffered before being forced to quit, he would have inflicted huge damage on the government and massively reduced his chances of a comeback.

And, with some Tory spokesmen whispering they were "after bigger fish", it was clear Mr Blair would have become increasingly targeted for failing to act.

As it was, Mr Mandelson acted swiftly and is far from finished as a significant political force.

Christmas comes early for William Hague

He still firmly believes he did nothing wrong, although William Hague's claim that he had broken Tony Blair's code for ministers is a powerful one.

And it is clear he had originally hoped to see off the storm.

He spent the whole of Monday in a frantic round of media interviews aimed at explaining his position and, he hoped, stemming the tide of criticism.

By the end of the day it was clear the strategy had failed and he told Mr Blair he felt he should resign for the good of the party and the country.

Mr Blair, who will feel the loss of his closest friend and confidante deeply, told him to sleep on it. But by the morning it was clear the row was not about to die down.

There was a second round of attacks in the press and the Tories stepped up their demands for his head.

Ironically, few actually believed he would be forced to resign and it is only with hindsight that it is clear he did the right thing both for his beloved party - which he virtually created ... and himself.

One of his great aims was to create a "whiter-than-white" party and he persistently warned Labour MPs and candidates that they should do nothing that could be portrayed in a negative light, no matter how innocent in reality.

He has done the prime minister a great service by finally abiding by his own rules and allowing him to draw a line under the row.

Tony Blair feels the loss of his friend

The Tories will still try to hit Mr Blair for failing to sack Mr Mandelson immediately, but the sting has been taken out of their tail.

Mr Blair has also made it crystal clear that he intends to bring Mr Mandelson back into the Cabinet in the future.

In his letter to him he declared: "In the future you will achieve much, much more."

In the short term, however, Mr Mandelson has lost most of his power and influence. He cannot be seen to be advising Mr Blair in any significant way because that would be seized on by the Tories.

And it will hurt him to be excluded from the "A list" of politicians, with all the trappings that go with that status.

It was that personal vanity which landed him in the mess in the first place through his desire to live a life out of step with his means.

His political future is now inextricable linked to Tony Blair's. If the prime minister continues to succeed then he will rehabilitate Mr Mandelson.

And it is even possible his dream of becoming Labour leader may be fulfilled, although that must be in some considerable doubt.