If Heathrow expansion is justified as growth for the whole country, its appraisal needs to support both parts of that claim. It should establish a credible national benefit and explain what can actually be said about where the benefit goes.
The economic modelling published by the Department for Transport in June 2026 gives us something more useful to examine than the word "growth" on its own.
Read the measure carefully
In the core scenario, annual real GDP in 2056 is estimated to be about 0.052 per cent above the no-expansion baseline. That is a difference in the level of GDP in that year. It isn't an extra 0.052 percentage points added to the growth rate every year.
The report describes relatively modest effects and explains that its passenger projections initially involve substantial displacement from other airports. It also models benefits through investment, trade and productivity. Those assumptions need scrutiny alongside the headline result.
The separate peer review raises concerns about claiming a broad regional distribution of gains from the modelling. That matters when regional benefit is part of the political case. A national estimate doesn't establish that each region benefits in the way an announcement might imply.
Displacement isn't the same as no benefit
Moving activity towards Heathrow may affect opportunities elsewhere. It doesn't follow that every job created there is a job destroyed in another region, or that relocation can never produce a national benefit. Different analyses need to explain their assumptions and distinguish jobs, passenger movements and economic output.
The government is entitled to argue that connectivity and investment justify expansion. Critics are entitled to ask whether those benefits have been overstated or distributed differently from the way the project is sold.
My objection is to treating appraisal as something that decorates an already settled decision. The figures should be capable of changing the case. If a benefit can't be established by the model, ministers should qualify the claim or provide other evidence.
Britain needs infrastructure. That is a reason to make better decisions about expensive projects, rather than a reason to stop asking what a particular one will deliver. A case for Heathrow can be made, but it should be the case the evidence supports.