Contrary to what you may hear today, David Cameron's plan for a "big society" threatens to undermine social justice and widen inequalities. While there is some effort to encourage people in poor neighbourhoods to do more for themselves, there is nothing in the plan to make sure that everyone – regardless of background or circumstance – gets a fair chance to participate or benefit.

Effectively, the "big society" abandons the idea of collective action and shared responsibility on a broad scale through the state, focusing instead on encouraging local interventions by the "little platoons" of civil society and businesses of all sizes. Individuals who are already marginalised by poverty and powerlessness will be left behind by the Big Society, where everything hangs on how much power is assumed by which groups and businesses, to do what, for whom and how. A much bigger role for the market is not a recipe for a bigger or stronger society, because in practice businesses – especially the big US corporations that are hovering over the NHS – are accountable to no one but their shareholders and much more interested in their financial bottom line than social justice or equality.

What's more, this scheme makes huge demands on people's time. A big part of the plan is to transfer power from state authorities to local groups so that they can do things on a voluntary basis that would otherwise be done by publicly funded organisations. Some people have much more time at their disposal than others. Individuals with low-paid jobs and big family responsibilities – especially lone parents – tend to be poor in time as well as money. Long hours and low wages undermine a key premise of the prime minister's vision, which appears to be that social and financial gains will come from replacing paid with unpaid labour.

Crucially, there are no central principles of fair play or equal opportunity. And even if there were, it is hard to see where we would find the means to enforce them. Local authorities and public regulators are being sliced down to the bare bones. And the very things that help to build equal opportunity and well-being for all – such as decent benefits for people out of work, housing support, child care, facilities for sports and recreation, not to mention free and fair education and healthcare – are all at risk from severe spending cuts.

What's needed is not just a transfer of power from the state to individuals and groups, but a new kind of partnership between citizens and government, where power and responsibility are shared on an open and equal basis between, on the one hand, professionals and other public service workers and, on the other, the people who are intended to benefit – especially those who are currently disadvantaged and disempowered. The central purpose of that partnership must be to promote social justice and to narrow inequalities. It should be about co-producing public goods and social benefits, not dumping on the poor. We shall also need to redistribute paid and unpaid time by moving towards a much shorter working week. There's already a big shift towards part-time working, which should be welcomed as a step in the right direction, not deplored as a short-term aberration. But it must be accompanied by things such as a higher minimum wage and flexible working conditions, to offset the effects on income for low-paid workers.

We don't want an overbearing state that depletes our capacity to help ourselves. But we do need a state that is democratically controlled, and that enables everyone to play a part and acts as an effective mediator and protector of our shared interests. Democratic government is the only effective vehicle for ensuring that resources are fairly distributed, both across the population and between individuals and groups at local levels. Businesses or third-sector organisations can supplement these functions but cannot replace them, not least because they invariably serve sectoral or specialised interests, rather than those of the nation as a whole. If the state is pruned so drastically that it is neither big enough nor strong enough to carry them out, the effect will be a more troubled and diminished society, not a bigger one.