In the very first speech after he was elected in 1997 Tony Blair told his Sedgefield constituents: "If we have done well then I know what this is a vote for. It is a vote for the future. It is not a vote for outdated dogma or ­ideology of any kind."

Say what you like about New Labour, it was never a moral project. Not that it set out to be wilfully immoral. But it was always determinedly amoral. Insisting that sticking to its principles was what had kept old Labour out of power, New Labour decided that it was better off without them. For its entire political life it has been defined more by what it is not than what it is. Ideologically it vowed to defeat the left, electorally it dedicated itself to defeating the Tories. Hardheaded, rather than soft-hearted, the primary case it made for itself was always strategic.

Absent any historic mission, like fighting inequality or protecting human rights, its central task was to win elections. This it did well, although not without some help from a weak ­opposition. Of his 1997 bid for power John Major later said: "If I had stood unopposed I would have come second." In 2001 William Hague was really ­standing for the leadership of his party rather than the country. In 2005 not even a swing of more than 20% to the Liberal Democrats would have delivered a majority to the Conservatives. This coming election will be the first time the Tories have been seriously in the game for 18 years.

That matters. Given the swingeing public sector cuts that will follow this recession, the next election will in effect decide who will wield the axe and be more responsive to the protests that will inevitably follow. If your primary desire is to keep them out of office then the strategic case for voting Labour has not been stronger for 17 years.

Clearly many people are too disgusted with Labour to even contemplate this. That is understandable. Keen to get my disillusionment in early and avoid the rush, I've been too disgusted to vote for Labour since 1992. What is difficult to understand is why people have chosen to become so disgusted with the party now.

Given the war-mongering, race-baiting, sophistry, scapegoating, attacks on civil liberties and complicity in torture, there was a far stronger case to oppose Labour on principle in 2005. With each passing day, the depths of mendacity reached by Blair before the war become clearer. News that he has been ­lobbying against an open and transparent inquiry into the Iraq war ­exemplifies both his desperation and contempt. He says he does not want to be part of a "show trial"; in essence he fears being exposed as a war criminal.

Compared to these outrages, ­Gordon Brown's period in office has been ­relatively tame. True, he has ­continued the occupations; but he has yet to start any illegal wars of his own. True, the state of the economy is bad; but the credit crunch is global. True, the expenses affair is vexing. But that is a parliamentary scandal – not a Labour scandal.

And while the details of their ­venality may be news, the fact of it is not, and no one is suggesting it is worse under Brown than anyone else. True, too, he handled it badly. But for the most part this was a matter of ­presentation rather than policy. Put bluntly, Brown may be terrible, but Blair was far worse. The moral case for voting Labour was ­certainly weaker in 2005 than it is now.

That is not saying much. New Labour set the bar low and has kept it there. Its record in winning elections is rivalled only by its knack for alienating electorates. It was "swept" to power in 1997 on the lowest turnout for more than 60 years and then re-elected in a ­"landslide" with the lowest turnout for more than 80 years. In 2005 it boasted the lowest share of the popular vote for any party that won a ­majority in ­Commons history. The party was ­tolerated, but never loved. As the ­co-architect of New Labour Brown has been complicit in everything Blair has done.

But it is saying something. Murder and torture do trump moats and tax dodges, and a Conservative victory would improve nothing. I can't help wonder what those former Labour ­voters who say they have never been more repulsed by Labour have been doing with their indignation since 2003, or what what outcome those who demand an immediate election seek beyond the return of a ­Conservative government.

The inherent weakness in writing this from New York is not lost on me. ­Keeping up with the news is not the same as keeping up with the mood. Not having lived in the UK for almost seven years and visiting a few times a year removes you from the human exchanges that give news meaning.

But distance can sharpen ­perspective as well as blur detail. Some of the most scathing attacks on Brown have come from those elements of the ­commentariat most invested in his ascendancy – a struggle that became more Byzantine the further you were from it.

Meanwhile, from this vantage point, when Americans following these events ask "why now?" and "what next?", I can only respond with a shrug. If the question is "How do you combat sleaze, confront political arrogance and check neoliberal policies?" then ­"electing Conservatives" sounds like a strange answer.

None of this adds up to a case for Brown or Labour. Iraq exemplified a profound dislocation between the nation's political class and political ­culture over which New Labour has long presided but for which it has never paid a price. The expenses scandal was in many ways emblematic of that ­cleavage – an aggregation of sleights rather than an escalation of them. Either way, the contempt the party has shown to its supporters and the nation is now being returned.

For New Labour to be worthy of office at this point it would have to show that it can reform itself – a task of which it has proved itself incapable. But having clogged or severed the democratic ­arteries within its body politic the party is now brain dead. The very impulses that would have given any talk of reform meaning have now gone.

To prolong this sclerotic deterioration by voting for it would simply entrench the popular cynicism and disillusionment not only in New Labour in particular but democratic politics in general that has contributed to the rise in the British National party. If you keep resorting to the lesser of two evils, you just end up with evil.

But it does add up to a case for a debate about policy and politics and genuine progressive alternatives that is not drowned out by anti-Labour and anti-Brown hysteria. We do not need a change of politicians or our political parties, but a root and branch upheaval in our politics – an electoral system through which we can vote for real change, a political class that can enact it sustained by a political culture that will stand for nothing less.

Labour deserves defeat – but the country does not deserve the ­Conservatives. So long as those are the only viable options disaffection will be the only viable outcome.