On Tuesday night, on the Budget vote, there was a Labour rebellion when some left-wing MPs voted against the Chancellor's tax cuts, rather than abstaining as they had been told to. Yesterday morning, this was hailed on television and radio as a personal triumph for the Labour leader.
It was a small rebellion, admittedly; and income tax is a particularly sensitive issue for the left - but a revolt is a revolt is a revolt. Ten disobedient MPs is surely a mild embarrassment? There were, after all, fewer whipless Tory rebels. Yet the general mood was, in Private Eye speak, large ones all round. Senior Shadow Cabinet people were talking of this as a turning point in Labour history. Well, as I say, there is no arguing with success. Hats off to Clan Campbell.
But are the implications that the hard left is now in effect dead - that the internal socialist challenge which has been a fact of life for all Labour leaders since the Fifties finally gone for ever? Persuading the public of this is extremely important for Blair as he sells Britain "new Labour". It may have been long ago, but memories of the Bennite uprising and union militancy are still fresh in the minds of many voters.
And the truth is that he has a compelling story to tell. It isn't only that the Campaign Group, formed in 1982, has never looked weaker. The hard left has always been weak in Parliament. It is more that the political and trade- union culture that allowed Labour leftism to flourish has largely disappeared. The proliferation of leftist groups inside the Labour Party, the moral force of CND during the Cold War, the powerful union shop stewards' committee and the culture of industrial confrontation that gave all left- wing MPs their weekly cause and rally point - it has mostly gone.
The changes to the Labour Party pushed through by Neil Kinnock, John Smith and Tony Blair amount to a counter-revolution, which stripped away all the power centres built up by the left, virtually dismantling the annual conference as a serious policy-making event. The National Executive Committee, where once the hard left were the biggest group, has dwindled in significance. Real policy is decided by the leadership, in private; at times it seems that Labour policy on any given subject is simply what Tony Blair says it is.
All of this puts left-wing Labour MPs in a different position from the Bevanites, Tribunites and Campaign Groupers of earlier years. Some of them can still pack meetings. But by comparison with previous generations of leftists they are isolated figures. Many are getting on in years. The 10 rebels this week have an average age of 57, two are in their seventies, and the two youngest are in their mid-forties. It was hardly a teenage revolt.
Benn himself, now 70, remains the ablest and most interesting left-winger, and has a status and following independent of the fortunes of the left generally. In the Commons, his interventions on everything from procedure to the Bosnian conflict still draw MPs into the chamber - not something you can say about any other member. Nice though it must be to have achieved guru status, however, it is a comedown from the days when he was poised to take over the Labour Party. If you want to change the world, the last thing you need from the British parliament is its affection.
One could reasonably conclude from all this that the Labour left really is dead. Some senior Labour people certainly think that. One senior Shadow Cabinet member reckons that all but nine or ten of the current Campaign Group are "biddable" - keen for government office.
But it would be foolish for Labour modernisers to relax entirely. Pre- election politics is an unreliable guide to life in office. A leftist MP who attacks the leadership now would be accused of damaging the party's chances of ending 18 years of Tory rule. Under a Labour government with a decent majority, that pressure comes off a bit. Rebellion would become glamorous again. As the Tory Maastricht rebels discovered, media enthusiasm for vivid quotes from dissident MPs on the Westminster lawn is insatiable. The airtime and coverage gives any consistent, eloquent rebel a greater status in the country and better access to voters than the average minister of state - and without the paperwork.
So I think that if a Blair Cabinet is locked in confrontation with nurses, teachers or local government staff, it is reasonable to assume that the parliamentary left will rediscover its instincts. However discouraging Blair and Gordon Brown are now, there will be a time of inflated expectations and then of expectation dashed. There will be arguments about Europe and Scotland.
This is why Blair's compelling story is also an unfinished story. So far ahead, the size and danger of such rebellions are impossible to predict. But that they will happen is predictable.
And, in a way, they need to. The Commons is already greyly unrepresentative of the variety of British opinions - for instance, there is not a single well-known environmentalist MP, which is pretty bizarre. That is part of Parliament's problem. The less dissidence and conversation it contains, the less the Commons as an institution matters. Voting reform would mean a wider variety of opinions daring to express themselves. Until then, however, I suspect that we will see more, not less, fracturing of party discipline as MPs respond to the market for alternative voices.
So there is a question about the extent to which Blair could achieve all his centralist, pro-European and reformist ambitions for office on the basis of iron discipline. He clearly wants to. He is trying to forge a hard-edged parliamentary force to sustain him for 10 years or more. But even the Tories have found this discipline increasingly difficult. So what if it isn't possible?
I was very struck recently by hearing a mainstream centralist Tory MP speculate about what would happen if his party lost the 1997 election and chose, in his words, a "Portillo-type leader". He would not leave the Conservatives, he said. He had been in the party too long to do that. But he and his friends might act as a "disloyal opposition". If Blair proposed something on Europe or economic policy that they thought good for the country, they would be likelier to back him against his own left wing than to follow the Tory nationalist leader in the lobby against him.
An outlandish thought I know. Yet if small groups of leftists can vote against the party line, so can others. Is it impossible to imagine Blair riding different voting coalitions in the Commons on different issues, countering leftist rebellions on, say, constitutional votes by using Liberal Democrat support and turning at other times to pro-European Tories?
That is a kind of politics we can scarcely imagine today. It would return the Commons to the time before it was dominated by rigidly predictable two-party whipping. It would create a more fluid and more interesting parliamentary politics. And it would be, to use Blair's phrase of the moment, impeccably One Nation.