For over a decade, England's affordable housing system has leaned on Affordable Rent as its default product. Affordable Rent lets registered providers charge up to 80% of local market rent, compared with Social Rent, which is set through a government formula tied to property value, size, and local income levels and typically lands at 50-60% of market rent. That gap in income has always mattered to viability. It matters more now, because policy is actively pushing the sector back toward Social Rent, and the numbers behind that shift are starting to bite.
Affordable Rent was introduced in 2011 as a way to stretch a shrinking grant pot further: charge tenants closer to market rates, and a scheme needs less public subsidy to add up. It worked, in the narrow sense that more "affordable" homes got built. Between 2013 and roughly 2022, over 257,000 Affordable Rent homes were delivered in England against just 66,635 new Social Rent homes, and the country's Social Rent stock fell by around 200,000 units over the same broad period through Right to Buy, demolition, and conversions.
The trade-off is now widely acknowledged as too severe. Affordable Rent runs, on average, 30% higher than equivalent Social Rent nationally, and the gap is far worse in high-value areas: over 100% higher in parts of Surrey and London for larger properties. For many of the households on a 1.34 million-strong social housing waiting list, an "affordable" home priced at 80% of London or South East market rent isn't actually affordable at all.
The government's response is the Social and Affordable Homes Programme (SAHP) 2026-2036, which commits at least 60% of the roughly 300,000 homes it funds to Social Rent, backed by up to £39 billion of funding. That is a deliberate reversal of the Affordable Rent-led model that has dominated delivery since 2011.
The mechanism is straightforward. Housing associations and councils historically relied on higher Affordable Rent income, and to a lesser extent Shared Ownership sales, to make the numbers on a scheme work with a smaller grant contribution. Shift a larger share of units to Social Rent, and the rental income a scheme generates over its lifetime drops sharply, without a matching drop in the cost of land, construction, and financing.
Independent modelling puts a number on that gap. One recent industry analysis estimated an average subsidy requirement of roughly £169,000 per Social Rent house and around £249,000 per Social Rent apartment, dwarfing the average £64,000 subsidy per affordable home assumed under the outgoing 2021-2026 Affordable Homes Programme. Even sites with free land still carry a substantial funding gap under Social Rent, because land cost was never the main driver of the shortfall.
This is precisely why Section 106 agreements, the planning mechanism through which private developers deliver most "affordable" housing in England, have leaned so heavily on Shared Ownership and intermediate rent rather than Social Rent: those tenures are worth more to a registered provider and need less top-up funding to stack up. As government policy now pushes the mix toward Social Rent, that cross-subsidy has to come from somewhere else, either a bigger grant contribution, more borrowing against future rental income, or a larger drag on the land value and profit that a private housebuilder can extract from a site.
The Home Builders Federation's Viability Crunch report frames this as part of a wider squeeze. Registered providers have shown reduced appetite to take on new Section 106 units over the past two to three years, a market already under strain from frozen rents and new building safety costs, and the report identifies the further shift from Affordable Rent to Social Rent as compounding this problem by requiring an even higher level of cross-subsidy from developers, further impacting the viability of new schemes.
Centre for Cities' modelling reinforces the structural limit here: the amount of affordable housing that can realistically be funded through private cross-subsidy varies enormously by location, and pushing for a "generational increase" in delivery, especially in lower-value areas, cannot be achieved through cross-subsidy alone. It requires more direct public investment.
A few second-order consequences are worth flagging:
Land value absorbs some of the gap, but only up to a point. Just as with other new costs the HBF report catalogues, the traditional assumption that landowners will simply accept a lower price to keep a scheme viable is running into its limits. Push land values down far enough and sites stop coming forward for planning permission at all.
Grant funding and borrowing have to fill more of the hole. The SAHP's structure, including up to £39 billion in funding and £2.5 billion in low-interest loans for registered providers between 2026 and 2030, reflects an acknowledgment that Social Rent-led delivery cannot be funded through rental income and cross-subsidy the way Affordable Rent-led delivery was.
Rent convergence is a partial offset, not a fix. From April 2026, the ten-year rent settlement caps increases at CPI plus 1%, and a return of "rent convergence" is expected to bring in an estimated extra £6 billion in rental income for providers between 2026 and 2036, with the benefit concentrated in London and the South East and largely unavailable until 2027. It narrows the funding gap; it doesn't close it.
Delivery is already softening. Annual housing completions in England have drifted down to around 200,000, well below the 300,000-plus needed to hit national targets, and the affordable housing pipeline specifically is contending with reduced registered-provider capacity to acquire new units.
For private housebuilders, the practical impact is that Section 106 negotiations are getting harder, not easier. A scheme that pencilled out with an Affordable Rent-weighted tenure mix five years ago may no longer clear viability testing once local policy or a registered provider's business plan pushes it toward more Social Rent, all while material costs, the Building Safety Levy, Future Homes Standard requirements, and other new obligations are pulling in the same direction on the cost side.
The Home Builders Federation's broader argument, that there is a finite pool of land value available to absorb these pressures and it is being asked to do too much at once, applies squarely here. Social Rent is the housing type in greatest demand and delivers the deepest social benefit per home. It is also, under the current funding model, the hardest tenure to make viable without either a bigger public subsidy or a smaller return to the landowner and developer. Resolving that tension, through the scale of SAHP grant funding, rent policy, or a genuine review of cumulative development costs, will determine whether the shift toward Social Rent translates into more homes for the people who need them most, or simply fewer sites getting built at all.