Every day the Guardian publishes accounts of desperate poverty and attacks on welfare provision. We know of the food banks, the plight of disabled people and the housing crisis that affects so many. We know of the propaganda to make the poorest people scapegoats for economic failure. We recognise the hypocrisy of Cameron's "moral mission".

We know that housing support goes to rich landlords, that benefits for the working poor subsidise employers who pay poverty wages. We read that benefit fraud is a tiny fraction of the overall welfare budget, far less than unclaimed benefits, and is nothing compared to the amount lost through tax dodging. But as we rail against the injustice and hypocrisy, we fail to ask one big question. Where is our political fightback? It should be led by the Labour party but therein lies the problem.

The coalition parties proclaim the importance of the market economy. So does Labour. The coalition cuts back on public enterprise and prioritises the interests of big corporations and private companies. So did the last Labour government. Whenever workers organise to defend jobs, wages or conditions, who supports them? Not Ed Miliband or other Labour leaders. An open letter to Miliband from Labourite "intellectuals" published in the Guardian this week is as peripheral is it is self-important.

The demands of the competitive market are remorseless: reduce the cost of labour; privatise everything; remove protection from working people, and maintain a pool of unemployed to discipline those lucky enough to have a job. Trade unions are to be obstructed while the wealthy are courted in the hope that they will find a pliant, flexible workforce that is easy to exploit.

We see the consequences not only in the workplace but in our health service, in education, in all aspects of social care that mark a civilised society. We see it in the disregard for the environment, as in the current push to start fracking for shale gas, regardless of its impact. We have seen it in the illegal wars and imperialist invasions of recent governments. None of this is new. But where is our political representation?

Labour's rhetoric may be softer than the Tories', but its fundamental stance is limited by the same imperative: profit comes before all else. Can the Labour party be reclaimed? Or, rather, made anew into one that will represent the interests of the people?

History suggests it cannot. The high-water mark of 1945 is long gone. The many great achievements of that government have largely been dismantled, either with the collusion of Labour or directly by the party when it has been in power. The Labour left has all but disappeared, and even Tony Benn's voice is now sadly silent. A Miliband government will not reverse any of the privatisations in the health service or elsewhere. It will not take the railways back into public ownership – despite the popularity of such a move – or even reclaim Royal Mail.

The Labour party is part of the problem, not the solution. The Greens have many admirable policies, but we look in vain for a thoroughgoing analysis for fundamental change. We need a new voice, a new movement – a new party.

There are many thousands of campaigns for worthy causes – against hospital closures, to support the homeless, against environmental destruction, to protect the disabled, for human rights and civil liberties, to help those in need – the list is endless. Trade unions still represent millions of working people. There is a unity of interest among all these groups. Imagine what could be achieved if we all acted together.

Left Unity was formed a few months ago to work towards such co-operation. The task is considerable. We are used to working and campaigning within our own small organisations. The proliferation of radical newspapers is witness to that. But the need is urgent. If we don't act together, the poverty, exploitation and alienation will get worse. Where is the rage, asks David Hare. It's there, alright. People are certainly angry enough. But they need political leadership to give them hope.

Labour has taken as its slogan "one nation" – coined by a 19th-century Tory, Benjamin Disraeli. Disraeli had no intention of bringing about the changes to make that a reality. Neither does today's Labour leadership, wedded to a capitalist economy that creates class division. The Labour manifesto of 1945 would be a better inspiration. It promised "a socialist party and proud of it. Its ultimate purpose … is the establishment of the socialist commonwealth, free, democratic, efficient, progressive, public-spirited, its material resources organised in the service of the … people".

The Labour government of '45 chose not to be that party or realise that ambition. Its reforms were to provide an infrastructure for a capitalist economy, not to change society. The task is now to turn the words of the manifesto into a reality. Assert the public good against private greed. Do we have the ability to make it happen?

A new party must be democratic, principled and properly organised. It needs an analysis of contemporary politics with a set of immediate demands: an industrial strategy to create green jobs, a statutory living wage, a public housing programme and a cap on private rents, an end to all privatisation in the health service.

It is a list many can compile; but without political representation it is a futile exercise. Who will put it into effect?

Building a democratic party with volunteer activists is a daunting task. But if we leave the sidelines and, finally, work together, it might just be possible.

• Left Unity has a conference in Manchester on Saturday (29 March). Visit www.leftunity.org