Is this the end of the brothers' political clout?

The last trade union leader of any note to become a Labour MP was Frank Cousins, the pro-CND, left-wing general secretary of the mighty Transport and General Workers. It was only a generation ago but light years away from the case of Alan Johnson, the former postal workers' leader who was elected as MP for Hull West on 1 May. Cousins went straight into a top ministerial job. Given the power over the Labour Party that he repeatedly exercised through the TGWU's block vote, he would scarcely have settled for anything less. He was unmistakeably the union's man in the cabinet (he even made sure his union job went unfilled while he was in government so he could go back to it). And he would have been utterly bewildered to find Alan Johnson, 30 years later, drafting a Fabian pamphlet suggesting ways the unions could loosen their links with the Labour Party.

But that's just the point. It scarcely matters that having become an MP instead of a union general secretary at exceedingly short notice, Johnson decided not to publish the pamphlet after all. Nor did he or his union colleague and co-author Tony Young propose an end to trade union affiliation to the Labour Party. But what they did suggest in the draft, unearthed by my colleague Barrie Clement yesterday, underlines the extent of the change in thinking among the most intelligent union leaders since Cousins' day: that political activity and expenditure should be "far more independent of Labour", and suggests that it is not only "absurd" but damaging to the unions to regard Labour as the "political wing of the trade union movement". We're all used to being told that the union link damages Labour. Johnson's point was that it damages the unions at least as much. One of the main reasons that he didn't publish was that it had been intended as a distinctively trade union document; now that he was an MP, it would have looked like mere special pleading by a politician.

Johnson knows what he is talking about. Before the election he hired Sir Tim Bell, a ranking figure in the left's demonology, and waged a sophisticated and highly successful campaign against Port Office privatisation, which sensibly and almost exclusively concentrated on influencing Tory MPs. He has a powerful point to make about how trade union interests are best served. But the argument goes deeper than that.

It is easy to see now that the Seventies - when Jack Jones was judged in opinion polls the second most powerful man in Britain and the TUC economic department was as influential as the Treasury - was very bad for the unions. A lot of their future difficulties flowed directly from the huge scale of their political power then. First, because the use of that power in a democracy is massively unpopular: a survey of potential union recruits by the public employees union, Nupe, in the Eighties, showed that the biggest single reason for not joining was its influence on the Labour Party.

Secondly, if you're running the country - or think, as some union leaders thought through much of the Eighties, that they would be, once Labour came back to power - then there is much less incentive to change or to build an independent base by recruiting in notoriously under-unionised sectors of the economy. As a result, many British unions clung for much too long through the Eighties to the wildly illiberal closed shop, and indulged in macho posturing about keeping the law out of industrial relations. Meanwhile, their European counterparts were quietly pursuing minimum wages, legal workplace rights and industrial democracy.

The revival of these arguments has nevertheless come at a sensitive time. Some unions have been muttering about party reforms, which will mean an end to the theatrical knife-edge votes on matters of policy that we came to know and love during party conferences in previous Labour administrations. The most enlightened in the union leadership, like John Monks, the TUC's General Secretary, know that a return to the Seventies is neither possible nor desirable. But there are others who still cling fondly to the culture of the Cousins-Jones era. And they fear Blair is secretly planning, in the long term, to destroy even their reduced base in the party: 50 per cent of the conference votes, 11 seats on the national executive, 30 seats in the 175-strong National Policy Forum.

He isn't. Or rather, to ask whether he is is to ask the wrong question: one about means rather than ends. It's like the question of whether Blair will opt for PR in the Commons. The end is clear: to preside over a coalition of centre and centre-left interests that covers the swath of political territory between Michael Meacher and Kenneth Clarke, as richly eclectic as was the 19th-century Liberal party - or the US Democrats, as Tony Benn prefers - and with a lot of support from business and industry.

Everything else, therefore, is a second-order question. If that coalition can be assembled only in multi-party form, through PR, then so be it. But if Paddy Ashdown and perhaps even some of the left Tories can be gradually sucked into a single 21st-century Liberal Party by steadily extending modest shares of power, such as membership of Cabinet committees, then fine. Similarly, with the unions and their leaders; provided that they do not seek to use their block vote, or their seats on the national executive, or their clout in the National Policy Forum to recreate the polity of the Seventies, Blair will be relaxed. If they do seek to use party muscle to pursue vested interests, they will find Blair alarmingly unsentimental about preserving the links.

Healthy unions are a symbol of a free society. It's a fairly safe bet that societies that don't have them, like societies which don't allow a free press, are not the kind of societies that most of its citizens want to live in. But that has little to do with union influence in the Labour Party. No other trade union movement in a modern industrialised economy has seats on the policy-making bodies of a party. Yet the AFL- CIO - the American TUC - which historically forswore political affiliation, still decided to give $60m to the second Clinton campaign. It's no good invoking the fact that the unions invented the Labour Party - which they did. That Labour party was for one century only - due to assume the status of an also-ran as the millennium passes. As Johnson points out in his never-to-be-published Fabian pamphlet, union leaders who aren't uneasily shackled to the government of the day are not merely freer to use their union political funds "for their own campaigns and activities" - they are also freer to speak their minds. The issue isn't really whether Blair's Labour Party will get rid of the unions; it's that the unions ought to be getting rid of Labour.