Heathrow's third runway has one public justification, and it is growth. Strip away the talk of hub status and global Britain and what remains is a promise that building it makes the country richer, and that the country means all of it. The Department for Transport has now published the modelling behind that promise. The modelling does not say what the promise says.
Start with the headline number, because it is the department's own. The upper bound on the annual GDP effect, in the impact report published alongside the consultation, is 0.05 per cent. Not the boost to Heathrow, or to west London. To the United Kingdom, per year, from a 3,500-metre runway crossing the current line of the M25 at an estimated cost of £33 billion. The airport would go from 480,000 flights a year to as many as 756,000. For that, a twentieth of one per cent.
The claim that does the political work
The number that matters politically is not the size of the gain but its address. Whether the whole nation feels the benefit is one of the four tests the government itself set for approving the scheme, which is why every version of the pitch insists the gains travel north. The department commissioned a peer review of its own GDP analysis. The reviewer wrote: "In my view, it would be erroneous to claim a broad distribution of the gains from Heathrow to regions on the basis of the modelling."
That is not a campaigner talking. That is the checker the department hired, telling it that one of its own four tests cannot be met on the evidence it has, in a document published on the same day as the case it undercuts.
Run the department's modelling forward and you can see why. The New Economics Foundation's reading of it puts 15,200 aviation jobs by 2050 that would otherwise have accrued in the regions, and another 6,400 from other airports in London and the south-east, ending up at Heathrow instead. Birmingham alone is forecast to lose 7.5 million passengers a year, which the foundation equates to about 9,500 jobs foregone at the airport and down its supply chain. Almost 10,000 from the West Midlands. Those are not jobs destroyed. They are jobs relocated, and relocated to the most expensive corner of the country - which is the reverse of what every government of the last fifteen years has said it was trying to do.
The department disputes that reading and it has an answer worth hearing. It says the analysis leaves out more than 60,000 local jobs the expansion would bring, that up to 40 per cent of a £2.6 billion boost would land outside London and the south-east, and that Birmingham's passenger numbers are forecast to almost triple by 2055. Some of that may well hold. None of it touches the reviewer's point, which was never about how large the gains are. It was about whether the modelling can say where they go.
What appraisal is for
There is a pattern here and it is older than this runway. A department decides a thing should be built. It commissions the numbers. It publishes the numbers, in full, at length, on the same afternoon as a short statement that claims rather more than the numbers can carry. The long document is public and the short one is quoted. Nobody has lied. The appraisal has simply stopped being a test the project might fail and become a formality the project passes on its way out of the door.
The other documents in that release are not decoration either. Impact assessments put significant adverse effects on the health and wellbeing of up to three million people living nearby. MPs still have to approve the national policy statement before any of it is built, which means the material sitting in that consultation is not background reading. It is the evidence base they are voting on.
None of this is an argument against building. Britain's problem has never been too much infrastructure. Forty years of not building has left the country expensive, congested and slow, and the fix is to build - including things that are loud, disruptive and unpopular with the people nearest them. But growth has become a word ministers can say instead of a number they have to defend, and a project this size should be made to produce the number.
The case for the third runway may still be winnable. It would have to be won on trade, or on hub connectivity, or on something other than the distributional claim its own reviewer says the modelling will not bear. Until someone does that, the honest description of the scheme is a £33 billion relocation of aviation activity towards the part of the country that already has most of it, for a national gain the department itself puts below a tenth of a per cent.
That might still be worth doing. It is just that nobody has argued it yet.
An opinion of the house. The argument is ours; the record beneath it belongs to no one.
How this piece was made
How this piece was made. Every figure comes from documents published by the Department for Transport alongside its consultation on the Heathrow expansion national policy statement, and from reporting of those documents by the Guardian on 27 July 2026 (https://www.theguardian.com/environment/2026/jul/27/heathrow-expansion-would-take-jobs-from-other-uk-regions-third-runway), which is held in the site's own capture with a source URL and retrieval time. The 0.05 per cent annual GDP figure and the quoted sentence on regional distribution are the department's own impact report and its own commissioned peer review, not a critic's estimate. The job-displacement figures (15,200 regional, 6,400 other London and south-east, 7.5 million Birmingham passengers, about 9,500 jobs) are the New Economics Foundation's analysis of the department's modelling and are attributed as such; the department's rebuttal (60,000 local jobs, up to 40 per cent of a £2.6 billion boost outside London and the south-east, Birmingham passenger numbers almost tripling by 2055) is quoted from the same source and is given its full weight. Where the two disagree, both readings are on the page and the reader can weigh them. The scheme details - 3,500 metres, the M25 crossing, £33 billion, 480,000 to 756,000 flights, up to three million people affected on health and wellbeing grounds - come from the same publications. No claim is made here about the motive or conduct of any individual; the argument is about an appraisal process and the institutions running it.
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