There is a simple story to be told about this, and a complicated one.
The simple one is that Britain can manage only two real parties, one of them a governing party and one of them a party of aspirations - a dreaming party. To be the governing party, it is necessary to be pragmatic, to be united and to give at least the illusion of a sense of national direction.
But the party of aspirations, which doesn't have to be united or pragmatic, can have more of an effect on the country's actual direction. Labour has been in power for far less of the century than the Tories. But because socialism captured the intelligentsia and was the dominant political idea, Tory rule involved (until Margaret Thatcher) the slow implementation of socialist thinking - withdrawal from Empire, state welfarism, progressive taxation.
And today, the big parties are reversing roles. ''Labour'' is positioning itself as the pragmatic governing party; the Tories, or at least a lot of them, are becoming dreamers, natural oppositionists.
Blair himself uses the language of rebirth, youth and newness, but his policies emphasise continuity. The Thatcher union laws will stay; the moderate pro-Europeanism of the post-war period will be sustained; the state's share of national wealth will remain broadly the same; the Nineties anti-progressive backlash in education and law and order will be keenly pursued. Harriet Harman, Jack Straw, David Blunkett and Frank Field now belong, in effect, to a political movement which includes many moderate Conservatives.
The Tory right, meanwhile, is determinedly trying to create a new party of aspirations, campaigning for a radical shrinking of the state, the end of welfarism, a break with the European Union and the restoration of a vigorously nationalistic mercantile Britain.
John Major recognises the threat of this revivalism. Day by day he sees his own carefully-constructed position as the ''safety first'' leader of Sensible England eroded by rebel romantics. Week by week, Tory commentators and propagandists flock to the more exhilarating programmes of John Redwood and Sir James Goldsmith.
And that, by and large, is the simple story: New Labour, cleansed, moderate, pragmatic, takes over from the factional, divided Tories, who have become interesting but silly. It is good news for the Blairites, so long as they remain doggedly cautious - fit spokesmen for the great consensus.
The complicated story is less comfortable for Labour, however. We should remember first that the party of aspirations may not have power, but may still have great intellectual influence, even dominating the agenda.
What will the next decade bring in politics? I would be surprised if there weren't new downward pressure on the state; harder moralising about the poor; and the revival of English nationalism in an ugly temper. All these things are present in the national conversation today; all are potent ingredients for a new Tory oppositionism.
Clearly the danger for a Blairite administration is that it finds itself blown by an ideological wind that is not of its making. This happened, after all, to the post-war Tory administrations which inherited Attlee's Britain; why shouldn't it be the fate of a post-Thatcherite Labour government?
And the only defence is a secure and radical agenda, a sense of direction that is clear enough to keep ''Labour'' on course. Its young, hyperactive leader himself has no doubts. He asks insistently whether it is likely that someone who has done so much while in opposition would be passive in power.
Change Labour; then Britain. But honouring that promise of radical government means answering the question we started with; what is ''Labour'' now for?
The only plausible answer is that far from being a status quo party, enjoying its time in the sun, it exists to shake the country up, breaking down excessive accumulations of power at the centre and defending the rights of the smaller platoons. Certainly that means the political reform agenda, which the Liberal Democrats currently lead.
But there is also an economic agenda that is radical, not socialist. As Britain becomes a relatively smaller player in the global economy, so fewer and bigger companies will dominate the country and, thus, its policy-making. We are half-way there and the danger of us becoming a chums' nation, in which cronyism finally replaces democracy, is real.
The rise of the private lobbyists, party funding rows and the silent power of company-influenced quangos are examples of how the spread of power in the economy affects mainstream politics. And the behaviour of privatised utilities; the swelling up of monopolies; European cartels; consumers' rights; and competition law are among the key new battlegrounds between those with too much power and those with too little. The distribution of power matters more than a penny on, or off, income tax.
No exhilarating language exists for this. We are still struggling with the politics of the Nineties via words and ideas from earlier generations. It doesn't matter. We will know a radical government when we see it - inverted commas or not.Reuse content