If we are serious about 1.5 million homes, we need to ask a different question.

We often talk about planning obligations as though each requirement can be considered in isolation.

It can't.

A developer has a finite residual value from which to fund land, construction, finance, tax, affordable housing, highways, education, open space, CIL, S106, the new building safety levy and an acceptable return.

When viability is tight, increasing one obligation inevitably puts pressure on another. This matters because we may now be asking developers to fund new infrastructure contributions while local authorities are sitting on billions of pounds of contributions that remain unspent.

The Home Builders Federation research ( https://www.hbf.co.uk/research-insight/unspent-developer-contributions/unspent-developer-contributions-2026/) estimates that around £9 billion of developer contributions is currently held unspent by local authorities.

That includes approximately £6.6 billion of S106 contributions and £2.2 billion of CIL. Almost £3 billion is estimated to have been held for more than five years.

Around £709 million of the unspent money is allocated to affordable housing with a further £2 billion allocated to schools and education. Not every pound sitting in a council account can simply be repurposed. Contributions are often tied to particular purposes, projects and contractual arrangements. They do, however, raise a fundamental question.

When a development is marginal, should an existing pot of unspent infrastructure funding be taken into account before reducing the affordable housing that a new scheme can deliver?

The SME problem

This is particularly important for SME developers. A national housebuilder can look at development economics across a substantial portfolio. An SME is often looking at one site.

If the numbers do not work on that site, there is no portfolio to spread the problem across.

The reality is often that something must give. In a viability negotiation, affordable housing can become the most obvious variable. Consistently an element of the affordable housing is removed from a scheme because the residual value cannot support every competing obligation while significant sums already paid by developers for infrastructure remain unspent.

I am not suggesting that infrastructure contributions are unnecessary. They are an important part of ensuring that new development provides the infrastructure and services that communities need. 

The question is one of priority. If the Government is serious about its ambition to deliver 1.5 million homes, I think three things need greater attention.

First, viability needs to start with deliverability.

The question should not simply be: What obligations can this scheme be required to provide?

It should also be: What can this scheme realistically provide while remaining capable of being built?

The HBF estimates that cumulative policy costs, taxes and inflation have added around £76,000 to the cost of building a home since 2020. The development appraisal is already carrying a significant burden before the next planning obligation is negotiated.

Second, existing infrastructure funding should be part of the conversation.

If an authority is holding substantial sums for a particular category of infrastructure, why should a marginal new development automatically be required to make another contribution? That doesn't mean existing funds should simply be transferred from one purpose to another. It does mean that the planning system should ask whether further contributions are genuinely necessary, proportionate and deliverable in the context of what is already held.

Third, transparency needs to improve. Developers and their advisers should be able to see, in a meaningful and accessible way:

- what developer contributions an authority holds;

- what they are allocated to;

- how long they have been held; and

- when the relevant infrastructure is expected to be delivered.

The HBF's research suggests that local authority reporting compliance has actually fallen with only 75% of authorities providing the requested information. That is not a minor administrative issue. It goes to the heart of whether the system is allocating scarce development value rationally.

Better information could make a real difference. If significant contributions have been collected but infrastructure remains undelivered that information should create pressure on an authority to explain when and how that infrastructure will be provided.

Equally, if the evidence shows that existing contributions are sufficient to address the relevant infrastructure need it should support an argument that a further contribution is unnecessary, disproportionate or a reduction should be considered.

This approach could help both delivery and viability.

A question of priorities

None of this is an argument against planning obligations. It is an argument for being more considered about them.

If a scheme has limited residual value, every pound allocated to one obligation is a pound unavailable for another. So why should affordable housing be the first casualty when other infrastructure contributions may already have substantial unspent balances sitting elsewhere within the system?

If we genuinely want a presumption in favour of development, it needs to mean more than supporting the principle of building homes. It needs to influence the way we assess what a viable development can actually provide.

The real question is not what can be extracted from a developer or development. Instead, a local planning authority should ask what combination of obligations will allow the development to happen while delivering the greatest benefit to the community.

A site sitting idle delivers nothing.