Less than two months into Southwark’s new Liberal Democrat-Green Joint Administration, we’ve secured an encouraging early win.

One of our first decisions was to support the legal challenge against the Mayor of London’s proposal to reduce the affordable housing threshold from 35% to 20%. That proposal has now been dropped. It is welcome news for everyone who believes London’s housing crisis will not be solved by making fewer homes affordable.

For us, this was about more than planning policy. It was about what kind of politics we want to practise.

Southwark faces one of the most acute housing crises in the country. Thousands of families remain on the housing waiting list. Thousands more are living in temporary accommodation. Young people who grew up here increasingly cannot afford to stay. Key workers are being priced out of the communities they serve.

Against that backdrop, reducing expectations for affordable housing was never the answer.

That doesn’t mean opposing development. Quite the opposite.

Liberal Democrats should be unapologetically pro-development. We need significantly more homes. We need private investment. We need housing associations, SME builders, institutional investors and especially councils all playing their part in increasing supply.

But development should be a means to deliver better communities, not an end in itself.

Too often, housing debates become polarised between those who oppose development altogether and those who argue that any development is good development. Neither reflects the challenge we face.

The role of progressive and liberal local government is to get homes built while ensuring that growth delivers public benefit. Homes must be what local people can genuinely afford. New neighbourhoods must have the infrastructure, green space and community facilities people need. Development should leave places stronger than it found them.

That is why I found the Labour Government and Mayor’s original proposal so disappointing.

Its logic was essentially that if affordable housing requirements were lowered, more developments would become viable and more homes would be built overall. It is a familiar argument and one rooted in the belief that relaxing social obligations on the market will ultimately produce better outcomes.

Sometimes described as pragmatism, it is in reality a distinctly neoliberal (some might say Thatcherite) approach.

There is nothing inherently progressive about reducing affordable housing expectations in the hope that the market will deliver social justice later.

Labour’s response to the housing crisis appeared to be lowering ambition. Ours is to ask why councils are being prevented from delivering the homes communities actually need.

The previous Labour administration in Southwark repeatedly failed to meet Government housing targets. That should not lead us to conclude that affordable housing expectations are too high. Instead, it should force us to confront the deeper barriers to delivery.

If we are serious about tackling the housing crisis, councils need the powers and resources to build again.

That means reforming the finances of council housebuilding. It means long-term certainty over funding. It means planning policies that support delivery while protecting affordability. It means treating councils as delivery partners, not simply regulators of private development.

As Liberal Democrats, we should reject the false choice between building homes and building affordable homes.

We can do both.

In Southwark, our Joint Administration wants to demonstrate that there is another way: one that embraces development, works constructively with the private sector and housing associations, but never loses sight of our responsibility to stand up for residents rather than simply accepting what the market offers. We also want the power so we will will build the thousands of new council homes our residents need.

Private development has an essential role to play. Profit is not a dirty word. But when private profit comes ahead of delivering social justice and meeting the housing needs of our communities, we have failed in our duty as public servants.

Our ambition is simple. We want Southwark to be the progressive, social liberal council that our borough wants and needs.

Supporting this legal challenge was an early example of what that means in practice. There will be many more to come!

* Victor Chamberlain is the Liberal Democrat Deputy Leader of Southwark Council, Vice Chair of Federal Council and Liberal Democrat Vice Chair of the Neighbourhoods Committee at the Local Government Association