Imagine yourself on the banks of a fast-flowing river. The water is full of people being swept along, in danger of drowning. You and others are trying to haul them out. It is unrelenting work but at some point, someone asks, "What's going on upstream? Shouldn't we find out why these people are falling in?"

This is a well-worked metaphor for much of the British welfare state. Another oft-quoted metaphor is the idea of building relatively inexpensive fences at the top of the cliff rather than running costly ambulances at the bottom.

It's not as though the idea of "prevention" and "early action" has lacked airtime – the coalition government has pledged to set up an early intervention board. But the concept remains limited, associated in most minds with action aimed at the under-fives and at troubled families – such as parenting classes.

If the idea of prevention from harm is to have real meaning, the concept must be placed at the very centre of social policy thinking. That is a tall order, because it requires a willingness to tackle rising inequalities head-on.

My interest in the importance of prevention comes from work I have done on security, fear and distrust; researching the links between high-security environments and soaring fear of crime.

Fear of crime is a very important issue for politicians and policy-makers, who have attempted to reassure the public through a combination of CCTV, the roll out of private security and policies to "design out" crime. These measures ensure that high security now defines our public buildings, schools and social housing, with many housing estates resembling gated fortresses.

But the fear of crime is not linked to actual crime. It does not correlate with crime figures but with levels of trust, and very often these high-security solutions undermine trust between people and, in fact, increase fear.

The New Economics Foundation thinktank is launching a programme of work on the wisdom of prevention. It splits prevention into "upstream" measures that aim to prevent harm before it occurs and that focus on system change, which means tackling growing inequalities, poverty and polarisation of our communities. "Midstream" measures aim to mitigate the effects of harm that has already happened and focus on groups considered at risk or vulnerable – such as troubled families. "Downstream" measures cope with the consequences of harm.

Most social policy interventions focus on downstream or, at best, midstream measures, such as early action work targeting troubled families. Increased security is a downstream solution to fear of crime, which risks making the problem worse. Without tackling the underlying causes of harm, midstream and downstream measures can have little or no lasting effect.

Prevention, taken seriously, does not shirk the issue of rising inequality. It requires systemic change in every sphere across the policy spectrum.

• Anna Minton is the author of Ground Control and is chairing the Wisdom of Prevention conference in London