In 1959, in the wake of Labour's third successive general election defeat, Hugh Gaitskell launched his bid to reform the old Clause IV of the party's constitution. Labour must adapt, he said, 'to be in touch always with ordinary people to avoid becoming small cliques of isolated, doctrine-ridden fanatics, out of touch, with the main stream of social life in our time'.

While Gaitskell's attempt to change Clause IV was unsuccessful, his speech captured well the essence of the party's revisionist tradition - that is, the belief that while values remain constant, the means to attain them must be kept constantly under review in the light of changes in society.

The notion that, as Gaitskell put it, the party should not, "wave the banners of a bygone age" was precisely the argument that Labour's revisionists of the 1980s and 1990s - Neil Kinnock, Tony Blair, and Gordon Brown - made to the party and which set it back on the road to electability.

Without revisionism, Labour might have ceased to exist, clinging to what Kinnock famously denounced in his 1986 conference speech as policies that are 'out-dated, misplaced, irrelevant to the real needs'.

The case for the continuing relevance of New Labour - with its insistence on the necessity of separating means from ends - hinges on its proponents' acceptance of this place within the revisionist tradition. As the shadow foreign secretary Douglas Alexander argues in the forthcoming issue of Progress magazine, New Labour was "composed of positions, personnel and policies". The personnel have changed and the policies for the 1990s are not going to be the solutions to the problems in the 2010s. But the positions - a determination to prioritise credibility on the economy, to stick to the centre-ground, and a willingness to take bold steps on issues like crime and antisocial behaviour - are ones we reject at great cost.

But New Labour, too, must itself guard against becoming a conservative force, stuck in the world of 1994 rather than 2011. Indeed, Labour's revisionists have made this error before.

Writing in the aftermath of Labour's fourth general election defeat in 1992, the historian David Marquand noted that, 'the values embodied in the ... social democratic middle way - a combination of personal freedom and social justice; of individual fulfilment and public purpose - are as compelling as they always were. But ... the instruments through which the revisionist social democrats of the 1960s and 1970s tried to realise their values broke in the hands of the governments which relied upon them.'

For many, this would be an apt description of New Labour's final years in government. And the solution that Marquand proposed nearly 20 years ago is as relevant today as it was then: 'If revisionist social democracy is to recover intellectually as well as politically, if it is to serve as a governing philosophy after an election as well as providing a platform from which to fight one, it must itself be revised.'

It is as a first contribution to what we hope will be a much-needed new chapter in the story of Labour's revisionist tradition that, alongside Biteback publishing, Progress today publishes The Purple Book.

The book rests on a belief that we need a 'revising of New Labour' and that this requires four things. First, a willingness, in the words of Ed Miliband, to escape the 'false choices' around Labour's electoral strategy. Second, an honest account of New Labour's period in office and its lessons. Third, a willingness to confront the division within the left on the role of the state. And, finally, the development of new policies - guided by the principle of redistributing power - to confront the new challenges facing Britain over the next decade. Crucially, these must be explicitly based on a recognition of the need to restore the public's shattered faith in the ability of the state and the market to widen opportunity, demand responsibility, and strengthen communities.

Comparisons have been made between The Purple Book and The Orange Book. Both attempt to revive a tradition from our respective parties' history that we believe has relevance for the future. But while The Orange Book attempted to revive economic liberalism, The Purple Book attempts no such thing - this has, after all, never been part a central part of Labour's story. We, instead, attempt to revive Labour's decentralising tradition of participation, self-government and "moral reform".

It is the tradition of those such as the Levellers and Thomas Paine who fought and argued for a widening of political rights; of the ethical socialism of RH Tawney and the guild socialism of GDH Cole; of the cooperative movement, Robert Owen, the Rochdale Pioneers and William Morris; of the self-organisation ethos by which the working class built the early trade union movement, the friendly societies and other institutions that reflected their belief in self-help; and the municipal "gas-and-water socialism" of the interwar years.

However diverse this tradition, there is a common thread running through it. Resting on the principles of participation and self-government, it challenges the approach that says that Labour's role should be to win elections, seize the commanding heights of the state and use power to redistribute resources from the few to the many.

Instead, the decentralist tradition requires the left to "create new centres of governance, power and wealth creation, as an alternative to both the centralised state and the private sector". This should be the guiding objective of a future Labour government, and the narrative with which the party describes its mission. The Purple Book begins to set out how.

Robert Philpot is the director of Progress.