A bold promise to dedicate half of all new homes in London to social housing has set up a clear dividing line in the capital’s housing debate, placing a mayoral hopeful on a collision course with City Hall policy.
In a campaign speech last week, Polanski vowed that at least 50 per cent of new housing developments would be reserved for social housing, alongside proposals for national rent controls—measures that would mark a significant intervention in the market.
The pledge stands in stark contrast to the approach taken by Sadiq Khan, who moved in October to reduce the capital’s social housing requirement from 35 per cent to 20 per cent to accelerate overall housebuilding.
City Hall has argued that reducing the quota would unlock stalled developments and boost supply at a time of acute housing need. Critics, however, say the shift risks weakening commitments to affordable housing in one of the world’s most expensive property markets.
Polanski’s proposal goes in the opposite direction, prioritising affordability over volume—but raises immediate questions over funding and viability.
Developers have long warned that higher social housing quotas can render projects financially unworkable without substantial public subsidy, particularly given elevated borrowing costs and rising construction expenses.
Without additional government support, industry figures are likely to question whether a 50 per cent requirement could be delivered at scale or would further slow the pace of new building.
The debate reflects a broader tension in housing policy: whether to maximise the number of homes built, or to ensure a greater share is genuinely affordable.
With demand continuing to outstrip supply across London, the issue is set to become a defining battleground in the capital’s next election.
Maria Hallows, Partner and Head of Social Housing at Menzies LLP said: “London’s social housing shortage is well-documented.
“Rents are rising and demand is only growing, so the case for ambitious targets is clear. But ambition has to be grounded in what’s financially deliverable for a struggling sector.
“Without significant government subsidy, the unintended consequence of a 50% quota could be developers delay projects or decide to walk away from their land banks entirely, resulting in less social and market-rate housing, not more. Sadiq Khan’s 35% target didn’t work and had to be reduced to 20%, and that is hard evidence that 50% is unlikely to be achievable without funding the government cannot currently afford.
“Applying rent controls at the same time only deepens this contradiction. If the proposal targets private sector rentals, given that housing associations are already subject to strict rent regulation, the direct impact on affordable housing supply is less clear-cut.
“But private sector rent controls carry their own risks: they can deter institutional investment in new build-to-rent stock, reduce the incentive for landlords to maintain and improve existing properties, and in the longer term constrain the overall supply of homes available to rent. The danger is that a measure aimed at protecting renters today makes the supply problem worse tomorrow.
“There’s also a supply chain risk that shouldn’t be overlooked. Greater demand would mean greater reliance on the handful of national and regional contractors with the capacity to build at scale in the capital.
“Housebuilders are already facing record post-Covid insolvency pressures, rising costs and geopolitical uncertainties – and they will need to be assured of profitability before committing to large construction and development pipelines. The question is whether these proposals, however well-intentioned, can realistically be delivered without a funding settlement to match.”
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