The government's decision to back Heathrow Airport's third-runway proposal, including the highly complex rerouting of the M25 motorway, represents a substantial milestone for UK infrastructure policy. After years of political hesitation, legal challenge and shifting strategic priorities, ministers have taken a definitive step by choosing to re-adopt the Heathrow Airport Ltd (HAL) scheme as the preferred option for expanding national aviation capacity. Yet the announcement, while politically significant, does not mean the project is anywhere near the finish line. In legal and regulatory terms, the path ahead remains long, intricate and almost certainly contentious.
The first major issue is procedural. By selecting HAL's proposal as the basis for updating the Airports National Policy Statement (ANPS), the government has triggered a statutory review and consultation process. This is not a formality. Under the Planning Act 2008, any National Policy Statement governing nationally significant infrastructure must be subject to public and stakeholder consultation, parliamentary scrutiny and evidence-based assessment before it can be formally designated. Only once a revised ANPS is adopted can Heathrow submit a Development Consent Order (DCO) application, the mechanism through which planning permission for the runway and all associated works would ultimately be granted.
In practice, this means the expansion is far from a done deal. There now exists a meaningful and time-bound opportunity for interested parties, including affected local authorities, environmental NGOs, residents' associations, and community groups, to test the assumptions underpinning the government's renewed backing for expansion. This consultation stage will also require ministers to demonstrate that the updated ANPS addresses the defects identified by the Court of Appeal in 2020, when the earlier ANPS was ruled unlawful for failing to consider the UK's climate commitments under the Paris Agreement. Although the Supreme Court later overturned that judgment, the episode crystallised the legal complexity surrounding major aviation expansion in an era of net-zero obligations.
Second, the legal risk does not end with consultation. Once a revised ANPS is designated, it becomes open to judicial review. Challenges may focus on whether the Secretary of State has complied with statutory environmental duties, whether the evidence base meets the requisite standard of rationality, or whether ministers have taken into account all relevant considerations, including updated climate-science assessments, air-quality legislation, noise-exposure impacts and the implications for regional inequality. Previous litigation over Heathrow expansion showed that the courts are prepared to engage seriously with these issues. The 2019–2020 judicial review proceedings examined procedural fairness, climate-law compliance, environmental assessment standards and human-rights arguments relating to community displacement and air pollution.
The proposed scheme carries features likely to attract further scrutiny. Re-routing a major section of the M25, one of the busiest motorways in Europe, poses significant engineering, safety and environmental challenges. The large-scale compulsory acquisition of land, demolition of homes, and potential long-term disruption to local communities all create a fertile landscape for legal challenge. Objectors may argue that the cumulative environmental impacts, when taken together with existing noise, air-quality and congestion burdens in West London, have not been adequately assessed. Others may contend that the government's balancing exercise, between economic benefits and environmental harms, fails tests of proportionality or conflicts with evolving climate policies, especially in light of more ambitious carbon-budget commitments and the Climate Change Committee's repeated warnings about aviation emissions.
Third, the legal architecture itself may soon change. The government has already indicated a desire to streamline the consenting process for nationally significant infrastructure, including airports. Proposals reportedly linked to the forthcoming Planning and Infrastructure Bill include reducing the statutory period for judicial review of National Policy Statements and DCO decisions, potentially halving the time available for bringing claims. While ministers argue this will reduce delays and unlock
investment, such reforms raise fundamental constitutional questions. Judicial review is one of the few mechanisms through which communities and public-interest groups can challenge large infrastructure decisions that may reshape local environments for generations. Curtailing the time available for scrutiny risks tilting the system further toward executive discretion at the expense of public participation, environmental accountability and the rule of law.
If reforms proceed as trailed, litigants may face compressed timelines to assemble complex expert evidence, a challenge particularly acute for environmental cases involving climate modelling, air-quality analysis or cumulative-impact assessments. Any perception that procedural reforms are designed to insulate the expansion from effective challenge could undermine confidence in both the project and the legitimacy of the broader planning system.
Finally, it is necessary to view the Heathrow decision within a broader strategic context. Although framed as a discrete aviation policy decision, the third runway sits at the intersection of the UK's wider transport-infrastructure, economic-growth and regional-connectivity agendas. The Government has repeatedly spoken of creating a coherent long-term plan integrating airports, rail corridors, roads and freight connectivity. But such a strategy is sustainable only if underpinned by robust legal processes and credible environmental governance. If the Heathrow expansion proceeds without convincing assessment of climate impacts, or if mechanisms for challenge are constrained, public trust in infrastructure planning could be eroded. This would not only complicate Heathrow's path but may also weaken support for future large-scale projects, including rail upgrades, road-tunnel proposals or renewable-energy infrastructure.
In short: the government has opened a door on Heathrow, but nothing is guaranteed. For HAL, the announcement is a major strategic victory and a long-awaited step forward. For residents, local authorities and environmental organisations, the coming months remain a crucial, and arguably necessary, period to examine whether the scheme is lawful, proportionate and genuinely aligned with the UK's long-term climate and environmental commitments.
The author is Andrew Sanderson, Transport partner at law firm Kingsley Napley LLP
