According to the Global Footprint Network, every person in the UK uses the equivalent of 5 hectares of land and seathrough the food we eat, the products we use and the carbon we release, which has to be absorbed somewhere if it is not to accelerate global warming. Yet the UK’s “biocapacity” (our ability to absorb these impacts) is a little over 1 hectare per person. Our extravagance is a cost that others must bear.

Public luxury available to all, or private luxury available to some: this is the choice we face at all times, but especially at this election. It is the conflict between these two visions that defines – or should define – our political options. There is a significant difference between Labour and the Conservatives in this respect, but I wish it were stronger.

Labour, through its proposed cultural capital fund, will reinvest in public galleries and museums. It will defend and expand our libraries, youth centres, football grounds, railways and local bus services. Unlike the Conservative manifesto, which is almost silent on the issue, Labour’s platform offers a reasonable list of protections to the living world.

But it also promises to “continue to upgrade our highways” (shortly after vowing to “encourage and enable people to get out of their cars”) and to provide new airport capacity. The conflicts are not acknowledged. Progress in the 21st century should be measured less by the new infrastructure you build than by the damaging infrastructure you retire.

Labour also misses a wonderful opportunity in its plans to expand affordable housing, to promote accommodation that both revives community and makes better use of space. In co-housing developments, people own or rent their own homes but share the rest of the land. Rather than chopping the available space into coffin-sized gardens in which a child cannot perform a cartwheel without hitting the fence, the children have room to run around together while the adults have space to garden and talk. Communal laundries release living space in people’s homes. Carpools reduce the need for parking. Isolation gives way to conviviality.

More importantly, and less surprisingly, the Labour manifesto fails to acknowledge the left’s great conundrum: the environmental damage caused by efforts to create jobs through economic growth. Like the Conservatives, like almost every party everywhere (the Greens are a notable exception), Labour’s economic vision is based on the presumption that there are no limits. Both conservative and social democratic parties see the world as a magic pudding that can never be exhausted. They build their economic programmes on a fairytale.

And they have another unexamined premise in common: that money legitimately buys you the power to take what you want from the world. There is an almost universal assumption in politics that you have the right to help yourself to as much of the global commons (atmosphere, soil, water, fish) as you can afford, though this reduces what is left for other people to share. You have the right to occupy as much physical space as your money can buy, regardless of the restrictions this imposes on others.

Where does this licence arise? Even if private wealth were obtained through the exercise of virtue (an unlikely proposition at the best of times) or through enterprise and hard work (ever less probable, in this new age of inheritance and rent), it is hard to discern the just principle that translates this money into permission to acquire the space and resources on which other people depend for a decent quality of life. When and by whom was this permission granted? How does it correspond to our notion of equal rights, or our concept of democracy, which is based on an equal power to decide?

You will not find these questions asked in this election or in any other. They are fudged by recourse to the magical belief that there is enough space and resources for everyone to do as they wish, that infinite growth ensures that no one – when the parties’ economic promises are fulfilled – will need to intrude on the interests of others. Yet, on this finite planet, they are the questions that will determine not only the quality of our lives but our security and, eventually, our survival. The primary task of all far-sighted politicians should be to decide first how much we can use, then how it can best be shared.