Some social problems are so large that policy makers are able to make only annoyingly minor inroads into them in any sensible period of time. Sometimes people act as though rough sleeping is one of these issues. They say people sleeping on the streets will always be with us.

But the Blair/Brown government showed that this just is not true. Although it never managed to eliminate rough sleeping completely, it did substantially reduce it. The latest figures from Shelter show rough sleeping has gone up by 169 per cent since that government left office in 2010. So what lessons does that period offer us now?

Like so many social issues, the number one thing needed to successfully tackle it is political will. Of course a genuine desire for change is not the whole story – but without it, the government machine will play only lip service to any agenda.

This will was evident early in the Blair premiership. Reducing rough sleeping was made a priority from the start. In 1997 the Social Exclusion Unit (SEU) was set up, and homelessness was one of its key themes.

The SEU proposed tough targets for reducing numbers. It’s always a political risk to commit yourself very publicly to such a target, and, of course, the target culture of New Labour was sometimes accused of creating perverse incentives; but the government did it anyway, publicly aiming to cut rough sleeping by two-thirds. The PM himself was closely identified with the target.

And to really get things focused, a specific and powerful unit was set up to make things happen in Whitehall. This Rough Sleepers Unit (RSU), led by ex-Shelter deputy director Louise Casey rather than a civil servant, was powerful across several departments. This was vital, as the causes of rough sleeping, and indeed homelessness generally, are complex and involve the failure of many different systems.

The RSU tried to encourage different agencies to work together at a local level to tackle this complexity. It was also strongly evidence-led and looked hard at preventative work, including around mental health and addiction. There was also a focus on the institutions which disproportionately feed the flow into rough sleeping. These included the armed forces, people leaving prison and care leavers.

And of course the Treasury was supportive, so serious money was put into the area. This was partly through dedicated funding for anti-rough sleeping initiatives but also through giving sensible budgets to key players like local councils, and the probation services.

The result was that the number of people sleeping rough in Britain tumbled down, and stayed low until some inevitable rise as the recession began to hit after the 2008 global financial crash.

Of course, New Labour did not get everything right. Some would argue that the emphasis on rough sleeping detracted from less visible aspects of homelessness. That government chose to focus funding strongly on doing up the quality of the existing social rented sector, through the Decent Homes programme, when perhaps it should also have made sure more social ones were being built.

But the success of the early to mid-2000s shows what can be done. And it is a striking contrast to today.

The current government recently passed the Homelessness Reduction Act, which may help; but it puts obligations on already very stretched local authorities. We don’t know exactly what will happen as Universal Credit is rolled out, but so far tenants who claim it are more than twice as likely to be in rent arrears than those on the old system.

The reduction of rough sleeping and homelessness does not have a powerful supporter in government, with a Brexit distracted PM, and a Treasury less interested in social issues than it was under Gordon Brown.

So who will deal with the crisis this time around? It is the third sector and devolved areas, as much as central government, that has been developing interesting new approaches.

These include Housing First, a policy in which people are housed first and then their health and other issues addressed; this was piloted in the UK by Turning Point Scotland and other charities years before the government invested £28m in flagship regional pilots.

Charities are also pioneering trauma-informed approaches, which recognise and actively respond to people’s experiences; redesigning services around homeless people’s lives; and galvanising action through local partnerships, including in Greater Manchester and Oxfordshire.

Having moved on from government, I lead New Philanthropy Capital, a charity think tank and we want to see more of this. We have published a paper outlining where funders and charities can do more to intervene on the complex systemic failures that cause homelessness and rough sleeping.

But ultimately, without a supportive government, it’s hard to achieve much at scale. Many social policy problems are difficult. But sometimes the reason for failure is that we are not really trying hard enough.

Dan Corry is the chief executive of New Philanthropy Capital, and a former head of the Number 10 Policy Unit.