Airport Stories
Heathrow’s Third Runway: Twenty Years of “Yes, No, Maybe”
Heathrow handled about 83.9 million passengers in 2024, making it one of the busiest airports on Earth. It does that with just two runways. For comparison, Paris Charles de Gaulle has four, and Amsterdam Schiphol has six.
Everyone in British aviation has known for a generation that Heathrow is full. A government first backed a third runway in 2003. Since then the plan has been approved, cancelled, studied, voted through, declared unlawful, declared lawful again, paused and relaunched. In September 2026 Heathrow said the runway might not open until 2039. That would be more than 35 years after the idea first became official policy.
How did one runway become one of the longest-running infrastructure fights in Europe?
What “full” actually means at Heathrow
Heathrow isn’t full because the tarmac can physically take no more aircraft. It’s full because of a legal cap. A planning condition attached to Terminal 5 limits the airport to 480,000 flights a year, and in recent years it has operated at about 98% of that. That works out to a take-off or landing roughly every 45 seconds at peak times.
Running that close to the limit has real consequences. There’s almost no slack in the schedule, so one bad-weather morning ripples through the whole day. And because take-off and landing slots (permission to use the runway at a particular time) are so scarce, they’ve become extraordinarily valuable. Airlines have paid tens of millions of pounds for a single pair of daily slots. New routes get squeezed out, which is one reason Heathrow has fewer connections to smaller cities than hubs like Frankfurt or Amsterdam.
The real numbers
Heathrow, in real numbers
83.9m
Passengers in 2024
On just two runways
480,000
Annual flight cap
Set by a Terminal 5 planning condition
~98%
Of the cap used
Almost no spare capacity
~756,000
Flights with a third runway
Heathrow’s own projection
Why it keeps stalling
The runway would be built to the northwest of the current airport. That sounds tidy on a map, but in practice it means crossing the M25, Britain’s busiest motorway, and demolishing much of the village of Harmondsworth. It also means putting a new flight path over parts of west London that currently have little aircraft noise.
So the project faces opposition on three fronts at once:
- Noise and local communities. Hundreds of thousands of people already live under Heathrow’s flight paths. The airport alternates which runway handles landings during the day so residents get predictable quiet periods; a third runway changes that pattern.
- Air quality. The area around Heathrow already struggles with pollution from road traffic, and more flights mean more cars and lorries too.
- Climate. The UK has legally binding carbon targets. Opponents argue more flights make them harder to hit. That argument won in the Court of Appeal in February 2020, before the Supreme Court overturned the ruling in December the same year.
Every new government, and every change of prime minister, has had to decide whether to spend political capital on those fights. Several decided not to. That’s why the timeline below looks like a see-saw.
The arc
The third runway, from first approval to 2039
- 2003The bet
Air Transport White Paper
The government backs a third Heathrow runway, subject to strict air-quality and noise conditions.
- Jan 2009The bet
Labour government approves it
Expansion is backed, with a tentative opening date of 2015.
- May 2010Break
Cancelled
The incoming Conservative–Liberal Democrat coalition scraps the plan.
- Jul 2015Reset
Airports Commission recommends Heathrow
After three years of study, the independent commission picks a new northwest runway over Gatwick.
- Jun 2018The bet
Commons vote: 415 to 119
MPs approve the Airports National Policy Statement, the planning framework for the runway.
- Feb 2020Break
Court of Appeal: unlawful
Judges rule the government failed to consider its Paris Agreement climate commitments.
- Dec 2020Strain
Supreme Court overturns that ruling
The policy is found lawful — but by now the pandemic has put everything on hold.
- Jan 2025Reset
Chancellor Rachel Reeves backs it
Expansion is relaunched as a growth policy.
- Nov 2025The bet
Heathrow’s £49bn scheme chosen
Preferred over the rival Heathrow West proposal from Arora Group.
- Sep 2026Strain
Target slips to 2039
Heathrow says 2035 is hard to achieve given the planning process; it now aims for consent by 2029.
The planning system, step by step
Even with political support, a project like this has to pass through the UK’s process for “nationally significant” infrastructure. First the government publishes a National Policy Statement, a document that sets out why the project is needed and how it will be judged. A draft Heathrow statement went out for consultation in June 2026. Only once that is finalised can Heathrow apply for a Development Consent Order, which is the actual planning permission. That application involves a public examination, then a ministerial decision, and very often a legal challenge afterwards.
Heathrow’s own position in September 2026 was that it hopes to have consent by 2029, with construction taking around a decade. That’s where the 2039 date comes from. Nothing about it is guaranteed; the project has been here before.
What happens while London waits
The rest of the London system has been absorbing the growth Heathrow can’t. Gatwick, Stansted and Luton have all expanded, and in September 2025 Gatwick won approval to use its standby runway for regular flights. But those airports mostly serve point-to-point leisure traffic. They don’t replace what Heathrow does: gather passengers from all over the world and connect them onto long-haul flights, the hub-and-spoke model.
Hub competition matters here. Every passenger connecting in Amsterdam, Paris, Frankfurt, Dubai or Doha instead of London is revenue for a rival hub and its home airlines. That’s the core business case Heathrow and British Airways’ owner IAG make for expansion. The opponents’ case is that the costs to people living nearby, and to the climate, outweigh it. Twenty years on, that argument still hasn’t been settled.
Sources & Further Reading
- Expansion of Heathrow Airport — Wikipedia ↗
- The Heathrow Airport expansion timeline — Airport Technology ↗
- UK government backs Heathrow Airport runway expansion — International Airport Review ↗
- Heathrow Airport Pushes £49 Billion 3rd Runway Opening to 2039 — Aviation A2Z ↗
- No easy fix to airport capacity crisis — Heathrow Media Centre ↗
- Government approves Gatwick northern runway plans — Air Cargo News ↗
Common Questions
Frequently Asked Questions
When will Heathrow's third runway open?
Not soon. In September 2026 Heathrow said the runway could open around 2039, four years later than the 2035 date previously discussed. It aims to secure planning permission by 2029, with construction taking roughly a decade after that.
How much will the third runway cost?
Heathrow's overall expansion plan is costed at about £49 billion. That figure covers more than the runway itself, including a new terminal, moving the M25 motorway and upgrades the airport had already planned.
Why does the M25 need to move?
The new runway would be built to the northwest of the current airport, across the line of the M25. The plan is to realign the motorway so the runway can cross over it.
How many flights does Heathrow handle now?
It is capped at 480,000 flights a year by a planning condition, and has been running at around 98% of that cap. Heathrow says the third runway would allow up to about 756,000 flights a year.
Is Gatwick expanding too?
Yes. In September 2025 the government approved Gatwick's plan to bring its existing standby runway into regular use alongside the main one, after it is moved about 12 metres north. A legal challenge to that decision was later rejected by the Court of Appeal.