Section 24: When Your Largest Expense Stops Counting

Imagine operating a business where your largest expense is treated as though it barely exists. That is effectively what happened to many British landlords. Section 24 is one of the most consequential housing policies of the past decade. It is also one of the least understood.

The mechanics are surprisingly simple. Most businesses are taxed on profit: revenue comes in, expenses are deducted, tax is paid on what remains. Mortgage interest is normally considered an expense, because it is one. For individual residential landlords, Section 24 changed that calculation. Between 2017 and 2020, full mortgage-interest deductibility was replaced with a basic-rate tax credit. Limited companies remained unaffected. Individual landlords did not.

The implications are significant. A landlord can now find themselves paying tax on income before their largest cost has been fully recognised. This creates a peculiar outcome in which economic profit and taxable profit become increasingly disconnected. The property may generate little actual cash flow while the tax calculation suggests something very different. That matters because businesses ultimately survive on cash, not accounting constructs.

The debate surrounding Section 24 often focuses on fairness. We think a more useful framework is incentives. What behaviour does the policy encourage? The answer appears relatively straightforward. It favours incorporation. It favours scale. It favours professional structures. And it disfavours the traditional individual landlord model that dominated British housing for decades.

The evidence is visible throughout the market. Some landlords have restructured. Some have reduced leverage. Some have sold assets. Others continue operating under increasingly challenging economics. Regardless of the path chosen, behaviour has changed, which suggests the policy is accomplishing exactly what incentives typically accomplish. It is reshaping the market.

One of the more interesting aspects of the debate is the distinction between housing and ownership. Section 24 does not reduce the need for housing. It does not eliminate tenants. It does not alter the long-term demand for rental accommodation. What it alters is who can most efficiently own it. That distinction matters enormously.

Much of the discussion around housing policy focuses on supply, affordability, and tenant protections. Far less attention is paid to ownership structure, yet ownership structure often determines how capital flows through an industry. Policies that increase complexity tend to favour larger, more sophisticated participants. Policies that reduce flexibility tend to favour them too. Policies that change financing economics do the same. Section 24 does all three.

Whether that outcome was intentional is largely irrelevant. Markets respond to incentives, not intentions. What began as a tax change has gradually become something larger: a sorting mechanism that differentiates between ownership models that continue to work and ownership models that increasingly struggle to do so. Many landlords continue to view Section 24 as a temporary frustration. We suspect history will view it differently. It may ultimately be remembered as one of the policies that accelerated the professionalisation of British housing ownership. Not because it changed the asset, but because it changed who could afford to own it.