On 16 December 2020, the UK Supreme Court overturned a Court of Appeal ruling that had declared the government's Airports National Policy Statement (ANPS) for Heathrow expansion unlawful. The decision reinstated the ANPS, allowing Heathrow Airport Holdings Ltd. to resume the planning process for a third runway in the London Borough of Hillingdon. The scheme, estimated at roughly £14 billion, proposes a new 3,500-metre runway northwest of the existing two.
The legal battle had peaked earlier that year. On 27 February 2020, the Court of Appeal ruled the ANPS unlawful because it did not sufficiently consider the UK's obligations under the Paris Agreement on climate change. That judgment reset the entire planning process, halting a scheme that had already cleared a significant parliamentary hurdle. The Supreme Court's reversal meant the policy framework was back in place, and the proposal could once again seek consent through a Development Consent Order (DCO).
What follows traces the decades-long planning battles, the 2018 parliamentary approval, the 2020 legal challenges and their outcomes, and the current status of the DCO process as of December 2023.
The 2018 Parliamentary Vote
On 25 June 2018, the UK Parliament voted 415 to 119 in favour of the Airports National Policy Statement. That vote gave official backing to a third runway at Heathrow, an ambition debated for decades. The ANPS set out the national need for additional airport capacity in the southeast of England and designated Heathrow as the location for that expansion.
The vote was a major milestone. Previous administrations had commissioned multiple reports on airport capacity, including the 2003 White Paper on aviation and the 2015 Davies Commission, but none had resulted in a formal policy statement that could trigger a planning application. The 2018 vote provided that trigger, instructing that the ANPS be designated as the framework against which any future planning application would be judged.
Opposition to the expansion was immediate. Environmental groups, local councils, and London's Mayor Sadiq Khan argued that the ANPS failed to account for the UK's climate commitments. They would soon take their case to court.
The Court of Appeal Ruling: February 2020
On 27 February 2020, the Court of Appeal of England and Wales ruled that the Airports National Policy Statement was unlawful. The court found that ministers had failed to take into account the UK's commitments under the Paris Agreement on climate change when they designated the ANPS. The Paris Agreement, which the UK ratified in 2016, commits signatories to limiting global temperature rises to well below 2 degrees Celsius above pre-industrial levels.
The legal challenge was brought by Friends of the Earth, Plan B Earth, and five local councils, with support from London Mayor Sadiq Khan. Their argument was straightforward: the state could not lawfully adopt a policy that would increase aviation emissions without assessing how that increase squared with its climate pledges. The Court of Appeal agreed.
The ruling did not kill the proposal. It said ministers could reconsider the ANPS with proper regard for the Paris Agreement. But it effectively reset the planning process, sending the policy back for revision. For Heathrow Airport Holdings Ltd., the decision meant that years of preparation and billions of pounds of investment were on hold.
The Supreme Court Overturns the Appeal Decision
On 16 December 2020, the UK Supreme Court overturned the Court of Appeal's decision. It ruled that ministers were not required to take the Paris Agreement into account when designating the ANPS. The court held that the Paris accord was not part of UK domestic law and that the state had not acted irrationally or unlawfully in failing to mention it in the policy statement.
The Supreme Court's decision reinstated the Airports National Policy Statement. This meant that the planning process for the Development Consent Order could resume. The court did not rule on the merits of the third runway itself. It ruled only on the legality of the process by which the policy was adopted.
The outcome was a clear win for the government and Heathrow Airport Holdings Ltd. The legal challenge that had threatened to derail the scheme was removed. But the underlying question of whether the expansion was compatible with the UK's climate goals remained politically unresolved.
The Cost and Capacity of the Third Runway
The third runway proposal adds a new 3,500-metre strip northwest of the existing two runways at Heathrow. The expansion is estimated at approximately £14 billion. That figure covers construction, land acquisition, and associated infrastructure such as new terminals, taxiways, and road and rail links.
The Opposing Parties and Their Arguments
The legal challenge to the Airports National Policy Statement was brought by Friends of the Earth, Plan B Earth, and five local councils. London Mayor Sadiq Khan also supported the challenge. The main argument was that the ANPS failed to consider the UK's obligations under the Paris Agreement on climate change.
The Impact of the COVID-19 Pandemic
The COVID-19 pandemic hit the aviation industry hard. Passenger numbers at Heathrow fell by more than 80% in 2020 compared to 2019. The collapse in demand raised questions about whether a third runway was still needed. Heathrow Airport Holdings Ltd. reported significant financial losses and deferred capital spending.
The Current Status of the DCO Process
As of December 2023, the Development Consent Order application for the third runway has not been submitted to the Secretary of State. The Supreme Court's ruling in December 2020 reinstated the ANPS, removing the legal barrier to the planning process. But the DCO process itself is lengthy and complex.
What Happens Next
The third runway at Heathrow is not dead, but it is not moving quickly either. The Supreme Court cleared the legal path in December 2020, but the proposal still needs a Development Consent Order, private financing, and continued political support. The estimated £14 billion cost has not changed, and the capacity increase from 80 million to 130 million passengers per year is still the stated aim.
Key Facts
- Scheme: Third runway at London Heathrow Airport (LHR)
- Location: London Borough of Hillingdon
- Proposed runway length: 3,500 metres northwest of existing runways
- Estimated cost: Approximately £14 billion
- Parliamentary vote: 415 to 119 in favour of the Airports National Policy Statement on 25 June 2018
- Court of Appeal ruling: 27 February 2020, ANPS declared unlawful for failing to consider Paris Agreement
- Supreme Court ruling: 16 December 2020, overturned Court of Appeal, reinstated ANPS
- Legal challengers: Friends of the Earth, Plan B Earth, five local councils, supported by London Mayor Sadiq Khan
- Owner/operator: Heathrow Airport Holdings Ltd.
- Status as of December 2023: ANPS reinstated; DCO application not yet submitted
Frequently Asked Questions
Why did the Court of Appeal rule the ANPS unlawful in February 2020?
The Court of Appeal ruled that the government had not taken sufficient account of the UK's obligations under the Paris Agreement on climate change when designating the Airports National Policy Statement. The court said this failure made the policy unlawful.
What did the Supreme Court decide in December 2020?
The Supreme Court overturned the Court of Appeal's decision on 16 December 2020. It ruled that the Paris Agreement was not part of UK domestic law and that the government had not acted unlawfully by failing to mention it in the ANPS. The decision reinstated the ANPS as government policy.
Has the Development Consent Order been submitted yet?
No. As of December 2023, Heathrow Airport Holdings Ltd. had not submitted a DCO application to the Secretary of State. The company continues to work on the required plans and assessments.
How much will the third runway cost?
The scheme is estimated to cost approximately £14 billion.
Who opposed the expansion in court?
The legal challenge was brought by Friends of the Earth, Plan B Earth, and five local councils. London Mayor Sadiq Khan supported the challenge.
