Anyone noticed the real elephant in the room?

Forget Iraq, the legitimacy of a government built on little electoral support is the biggest political issue, says David Runciman.

Tony Blair went into his final Labour Party conference as one of the undisputed titans of British electoral history - deliverer to his party of three resounding parliamentary majorities in succession. The fact that he is in effect being driven from office within 18 months of the third of these victories strikes many of his supporters as not merely bizarre but almost inexplicable. Yet it is only inexplicable if one assumes that one decisive parliamentary majority is as good as any other. The truth is that Blair's third victory was different, not just from his first two, but from any other of recent times. It was achieved on a bare minimum of popular support, just over 35 per cent of just over 61 per cent of the electorate. So if you put 100 random adults in a room, you would find that only 21 of them voted Labour in 2005.

This, not Iraq, is the "elephant in the room" of British politics. Before the most recent election, there was serious talk at the highest levels of Government about a possible "crisis of legitimacy" if a substantial parliamentary majority was achieved on the basis of minimal voter enthusiasm. But when this happened, all such talk was forgotten in the excitement of watching what the Tories would do next and trying to decide how to respond.

However, the fact remains that the support of barely one fifth of the adult population is a very slender basis on which to seek to exercise the awesome discretionary powers of a British prime minister possessed of a sizeable majority in the Commons. Moreover, these are powers that Blair has not merely wished to employ to the full, but to which he has sought to add by claiming the further right to preordain the moment of his departure. It is this that has produced his personal crisis of legitimacy.

Nevertheless, for all its peculiarity, the predicament of the British Government is hardly unprecedented. Indeed, trying to govern on the basis of limited numbers of actual votes was the steady state of politics throughout the 19th century. This was the case even after successive reforms of the franchise, when governments had to sustain themselves on the electoral support of relatively small pluralities of the adult population (post-1884, 40 per cent of adult males and all women were still disenfranchised). In these circumstances, it was understood that governmental legitimacy depended on not overstating the significance of mere electoral success.JGovernments also had to rest their authority on the constant endeavour to fashion coalitions of the willing in Cabinet and in Parliament. The allocation of seats after a general election could only ever be the starting point, not the decisive end point, of such attempts.

This solution to its crisis of legitimacy is not available to the current Labour Government, even if it wanted it (and the aborted coup against Blair suggests that some members do) - you cannot play 19th-century politics in 21st-century circumstances, when the tiniest hint of party discord gets splashed across the 24-hour media and the privacy the Victorian elite needed to fashion and refashion governing coalitions beyond the prying eyes of the electorate has long since disappeared. It would be wrong to overstate the gentlemanly detachment of mid to late 19th-century politicians - their world was much closer to the hypocritical populism laid bare in Anthony Trollope's Palliser novels than to the liberal fantasies of John Stuart Mill, who wished Parliament to become a crucible of enlightened and independent opinion. But even in Trollope's world, the fuel of parliamentary infighting was the universal recognition that general elections were not everything - and it is that understanding that is now gone.

In its absence, the only plausible alternative to Labour's current predicament is reform of the electoral system to produce governing coalitions that better reflect the distribution of votes. But it is striking that, for all the weakness of his position, none of Blair's opponents is pushing for this. Neither Gordon Brown nor Tory leader David Cameron wishes to replace the system that produced Blair; they merely wish to replace him at its helm. The Liberal Democrats, traditional champions of proportional representation, see that the present system offers them the prospect of holding the balance of power after the next election in a hung Parliament, and they do not want to do anything to rock the boat before then.

So the roots of Labour's crisis of legitimacy will remain unspoken at their conference, while the attempts of those such as MP Clare Short to ventilate the issue will continue to be passed over with disdain. Meanwhile, the parliamentary plotters will carry on plotting behind the scenes, as though there still were a "behind the scenes", and as though independent-minded parliamentarians still determined the government's legitimacy. In the end, something will have to give: 19th-century politics in the 21st century simply does not work.

David Runciman is a politics lecturer at Cambridge University and author of The Politics of Good Intentions , published by Princeton University Press, £18.95.