The story, it seems, is fading. Christmas and war with Iraq will soon expel it from our screens and newsprint altogether. So how will the saga of the prime minister's wife, the conman and the topless model turned lifestyle guru be generally remembered? Almost certainly in exactly these sort of cartoon cut-out terms. As the media and even some of those most directly involved have represented it, Cheriegate has been essentially about personalities and their foibles and failings. No more than a simple tale, as Peter Foster put it, of villains and victims. The only point at issue, apparently, has been establishing who were the villains, and who - if any - were the victims.

Those who lean towards the right or merely dislike the Blairs have been inclined to identify Cherie herself as chief villain. She is a scheming, uppity, too-clever-by-half woman who dabbles in politics and has strange and unsavoury friends, they suggest. No wonder she lied. Pundits and polemicists on the left, meanwhile, have been more likely to pin the blame on unscrupulous Australians, on the male chauvinism of the Daily Mail, on Tory plotters, and on ravenous and rabid media hacks.

In neither case has analysis proceeded far beyond gossip and character assassination. Even those who have posed questions about the more abstract and political lessons of this affair have tended to interpret it only as a symptom of the particular characteristics and reputed flaws of the Blair administration, its excessive love of spin and its court of cronies. Yet Cheriegate ideally needs locating in both a much longer and a much broader context.

From a transatlantic perspective, for instance, what is most astonishing about this affair is that the busy wife of a prime minister has had to devote time to locating accommodation for one of her offspring, and has had to seek advice from a stranger and a private individual in the process. The British have focused on the criminal past of the individual involved, on his relationship with Cherie's friend, Carole Caplin, and on the possible impact of all this on his deportation.

But the primary response of any Americans viewing this business would probably be rather different. Why, they would be likely to ask, did Cherie have to trouble herself in this fashion? Where, for heaven's sake, were her staff? It is hard to imagine an American first lady in recent decades who needed to go to quite so much trouble directly over domestic details such as this. Just as it is hard to imagine Americans being quite as angry as many Britons have been about the children of their head of state requiring private and select accommodation at university.

To most Americans it would seem obvious enough that the son or daughter of a president would require a secure and special space away from home where he or she could be as protected as possible from potential kidnappers, terrorists, scroungers and voyeurs. So why is it all so different for Cherie and her family? The answer, of course, is that Tony Blair is not nominally a president. But neither do those who head British administrations function any more simply as prime ministers: and it is this radical shift in the nature of the office that lies behind much of the surface clutter, idiocy and miseries of Cheriegate.

For good or for ill, Britain is in some respects moving away from a prime-ministerial system towards a presidential one. This is emphatically not, as is sometimes argued, simply a function of Tony Blair's personal ambition. The shift towards a more presidential style was already visible under Margaret Thatcher. As global connections become more developed, as Britain becomes a more insignificant and dependent power, as more of our foreign policy is determined in Washington, and as more of our domestic business and economy are shaped by Brussels, the old national power games, systems and mythologies are bound to become more threadbare, insufficient and obliged to change. Irrespective of their party affiliation or wishes on the matter, those governing from 10 Downing Street now have to take on much of the aura and role of head of state. And this is bound to have heavy consequences for their family.

Even if Cherie harboured no interest in politics at all, she would still have to fulfil many of the functions of an American first lady. Consequently, one of the things that is needed now and in the future is more and better staff at number 10 specifically assigned to look after the prime minister's spouse and protect her or him from the sort of mess, muddle and unfortunate connections and communications that have been exhibited recently.

This point is paradoxically reinforced by a glance at the past. High-level political wives are by no means new. In the 18th and 19th centuries, when patricians dominated British political life, it was common for politicians' spouses to play an active political role. The wife of Lord Palmerston, who was prime minister twice over, for instance, regularly corresponded with her husband's ministers and minions on matters political, and held parties and soirees at which public business was conducted.

She and her kind were able to operate in this fashion, however, because they had access to abundant staff. Lady Palmerston had no emails at her service, but she did have servants aplenty to carry her messages far more discreetly, just as she had servants to manage her political dinners and to advise her on clothes. Many of Cherie's recent troubles have stemmed from the fact that, because of social changes as well as because of political changes, she lacks adequate auxiliaries to play the demanding and multi-faceted role that she is now obliged to inhabit as a prime minister's wife in residence.

But there is a final and far more significant point. British prime ministers and prime ministers' spouses and children are together becoming ever more like first families. They need to be given sufficient resources and personnel to enable them to carry out their shifting roles efficiently, decently and safely. But, by the same token, the British public and parliament also need better ways of scrutinising, monitoring and regulating that small outpost of the White House that is now situated at 10 Downing Street. They need more and better help; we need more and better controls. This is the more austere and less lubricious lesson of Cheriegate. Forget the gossip: it's about the constitution.

· Captives: Britain, Empire and the World, 1600-1850, by Linda Colley, is published by Jonathan Cape.