Following the fall of the second Labour government (1929-31), R H Tawney published a celebrated essay in Political Quarterly entitled "The Choice Before the Labour Party". He complained that the "degeneration" of socialist parties on assuming office was an old story and that what the party needed was not "self-commiseration" but "a little cold realism". Labour, he wrote, is "hesitant in action, because divided in mind. It does not achieve what it could, because it does not know what it wants. It frets out of office and fumbles in it . . . Being without clear convictions as to its own meaning and purpose, it is deprived of the dynamic which only convictions supply."

To reread Tawney's essay is to understand that the choice before Labour today is much as it was in 1931. If the party is to renew itself, once again to become the vital, progressive and reforming social-democratic force in British politics, it must first rediscover the language of conviction, as well as a guiding sense of its own meaning and purpose. Labour must play a lead role in the remoralisation of our politics; it needs to understand why so many of its natural supporters feel estranged from - or let down by - the party.

Over the months ahead, we shall be publishing some of our finest political writers as part of a larger debate on the future of progressive politics. All our party leaders recognise that something is rotten in our politics; they speak of the need for change but, too often, their positions are merely rhetorical. "Change" is the all-purpose cant word of our struggling political elites.

Since I became editor of the New Statesman in October 2008, I have, through our leader columns, been arguing for a realignment of liberal-left politics. The larger failures of the Blair-Brown years are everywhere apparent, from the obfuscations and divisions created by the Iraq war to New Labour's fatal embrace of neoliberalism; from deepening inequality to the erosion of our civil liberties. Progressive politics should be about the dispersal of power and opportunity. Labour has sought to centralise, control and command with its top-down, market-driven prescriptions. We need a more republican notion of freedom: freedom from domination and arbitrary power. Only now, in the final months of this government, has the party begun seriously to consider electoral reform and the abolition of the House of Lords. Too late, perhaps, already too late.

In the first essay in our series, Anthony Barnett, co-founder of Charter 88 and a bold advocate of the open society, argues trenchantly that the best outcome of the forthcoming election would be a hung parliament. In effect, he is saying that Labour does not deserve the support of progressives committed to political and constitutional renewal. John Kampfner, editor of the New Statesman from 2005-2008, argued similarly in his recent pamphlet Lost labours.

Unlike Barnett, we believe that the Labour Party remains the primary means by which to achieve a plural, social-democratic transformation. Ed Miliband, a contender for the leadership, said to me recently that New Labour "made its peace with capitalism, but did not offer a critique of it". At present, any number of good people within the party are beginning to offer that necessary critique of market fundamentalism. There is a sincere willingness to learn from what went wrong.

So, this need not be a time of quietism or abandonment: the Labour Party will serve Britain best by, as Tawney wrote, "clarifying its own principles and acting in accordance with them". Let the argument begin.