The Children Won

The most hated policy in modern British politics was vindicated this week, and the people it helped cannot even vote. On 18 August 2026, The Lancet Public Health published the CHILL study, a five-year natural experiment showing that London's Ultra Low Emission Zone measurably restored children's lung growth (Wood et al., 2026). The fight that convulsed the country in the summer of 2023 — the Uxbridge by-election, the "war on motorists", the Ulez expansion — was, at bottom, a fight about 3,400 children's lungs. The children won. And the detail that should change how every city in the world thinks about traffic is this: the damage was reversible, and the payback period was one school year, not one generation. Ten millilitres of lung capacity per child, per year, for life.

The Policy Everyone Hated

Remember July 2023. Uxbridge and South Ruislip, a by-election nobody expected to matter, swung on one word: Ulez. The expansion of the Ultra Low Emission Zone to outer London was cast as a "war on motorists", a tax on working people, a cost-of-living kick in the teeth. The Conservative candidate won. Labour's leader, who had backed the policy, scrambled. And every party in Britain drew the same lesson: clean-air zones are electoral poison. Touch them and lose.

Here is what the story left out. The measurable payoff of that hated policy accrued to children who cannot vote, cannot lobby, and cannot write angry letters to their MP. And the cost-of-living argument — the one that carried the by-election — was answered this week in the simplest currency there is: 10 mL of lung capacity per child per year, compounding for the rest of their lives. A lung is not a fuel bill. It does not come back when prices fall.

The Natural Experiment

Why should anyone believe this? Because CHILL was built like a controlled trial, minus the control. It is a natural experiment: 3,404 children aged 6 to 9, across 84 primary schools, measured annually from 2018 to 2022 — five years of lung-function readings on growing children, the very years the central-London Ulez was in force. The comparison city was Luton: similar traffic pollution, no clean-air zone, no intervention. Same age range, same measurement protocol, same years. The only meaningful difference between the two groups of children was the air they breathed — and the policy that changed it.

That design matters. A natural experiment cannot randomise a city, but it can do the next best thing: find two cities that look alike, change one, and watch. When the divergence shows up in children's lungs — not in survey responses, not in stated intentions — you are looking at physiology, and physiology does not lie to pollsters.

What the Numbers Say

Children with clinically impaired lung functionBaseline (2018) vs five years later (2022), % of childrenLondon (ULEZ)Luton (control)16%12%8%4%0%14%9%9%7%2018202220182022London (ULEZ)Luton (control)-5 pts-2 pts
The intervention city improved nearly twice as much. Source: Wood et al., The Lancet Public Health (2026).

The headline number: FEV1 — the standard measure of lung capacity — grew about 10 mL per year faster in London children than in Luton children. Not a one-off reading, but a growth rate, sustained year over year. Compound that across childhood and you get a real difference in adult lung function, the kind that shows up decades later as breathlessness, asthma severity, hospital admissions.

The second number is the one to sit with. The proportion of London children with clinically impaired lung function fell from 14% to 9% across the study period — a five-point improvement. Luton fell from 9% to 7%. The control city improved a little; the intervention city improved nearly twice as much. Meanwhile NO2 exposure fell twice as fast in London as in Luton — mechanism and outcome moving in the same direction. And by the end of the study, London children's lungs had caught up, becoming comparable with their Luton peers.

This is the rare policy result that is hard to argue with, because it is a reversal. The earlier cross-sectional work had found children in London's most polluted areas with roughly 5–10% less lung capacity by age 8–9 (Lancet Public Health, 2019). CHILL shows that capacity coming back.

The Uncomfortable Truth

Here is the part no political party wants to say out loud. The children who benefited cannot vote, and the adults who could vote were asked to pay — in the price of a journey, in the value of a car, in the inconvenience of a bus. The electorate was asked to trade a small, visible cost for a large, invisible benefit, and the benefit went to people without a vote. The surprise is not that the policy was hated. The surprise is that it worked anyway.

And here is the sharper point. You do not need to electrify every car to fix children's lungs. The EV-only framing of transport policy — battery factories, charge-point targets, showroom subsidies — has quietly become the only framing, and it misses the fastest health win on the board. Clean-air zones work by price: they make the dirtiest vehicles expensive to run in the places where children breathe, and the market does the rest, school run by school run. Electric vehicles are the long game. Clean-air zones are the health win available this school year. This is not an argument against EVs; it is an argument against single-lever thinking, and against pretending the future is the only thing worth buying with the present.

The Honest Caveats

The credibility of this result depends on saying what it does not prove. Stephen Burgess, a biostatistician at Cambridge with no involvement in the study, notes the Covid confounder: lockdowns shifted pollution in both cities, and you cannot fully separate the pandemic's effect from the zone's (Science Media Centre, 2026). The authors' counter is the cleanest one available — NO2 fell twice as fast in London, and children's lungs improved fastest in exactly the city where the policy was — but the caveat deserves its place.

Two more, honestly. Both cities remain above WHO air-quality guideline levels for NO2 — 10 µg/m³ annual (WHO, 2021) — so the win is partial. That is not a reason to shrug; it is the point. If a partial intervention bought this much lung function back, the remaining gap is a measure of what more ambition would buy. And the study covers children in the original central-London Ulez area — the zone that has existed longest. It does not cover the outer-London expansion that caused the 2023 political explosion, though the mechanism it validates is precisely the mechanism that expansion applies.

What Comes Next

The reactions wrote themselves: Sadiq Khan claiming vindication, health minister Karin Smyth welcoming the findings (The Guardian, 2026). The numbers do not need their endorsements. Professor Chris Griffiths (Oxford/QMUL), joint senior author of CHILL, put it plainly: "Ambitious clean-air zones should be considered a priority for cities globally with traffic-related air pollution." Not a nicety. A priority (Wood et al., 2026).

So the ask is specific. First, treat clean-air zones as public-health infrastructure, not transport policy — the evidence of benefit is now lung-function data, the same currency as vaccination programmes. Second, measure lung function, not just policy compliance: monitor children's respiratory health in every city with a traffic problem, so the next Ulez arrives with a pre-registered, publishable outcome. Third, stop letting the politics stand in for the science. The science picked a side this week. The children won — and the policy everyone hated is the policy that gave them their lungs back.

Sources

  1. Wood H, et al. (2026) — Impact of the Ultra Low Emission Zone on lung function growth in children in London, UK: a prospective parallel cohort study (CHILL), The Lancet Public Health, published 18 Aug 2026. DOI: 10.1016/s2468-2667(26)00163-5
  2. The Guardian (2026) — Ulez led to better lung size and function among London children, study finds, 18 Aug 2026 (incl. Sadiq Khan comment piece and health minister Karin Smyth). theguardian.com
  3. Science Media Centre (2026) — ULEZ and lung function in children in London briefing and expert roundup (incl. Stephen Burgess, Cambridge), 18 Aug 2026. sciencemediacentre.org
  4. WHO (2021) — WHO Global Air Quality Guidelines, 2021 (NO2 annual guideline 10 µg/m³). who.int
  5. Lancet Public Health (2019) — cross-sectional study of London's low emission zone and children's respiratory health (children from the most polluted areas had ~5–10% less lung capacity by age 8–9). DOI: 10.1016/s2468-2667(18)30202-0