Will Heathrow's third runway ever happen? And what will be lost if it does?
Plans to expand Heathrow Airport have been taxi-ing around for years without ever taking off. Heathrow is traditionally the busiest airport in Europe and the fourth busiest in the world by passenger numbers (2023 figures). Yet it only has two runways, and it was recently overtaken by Istanbul for number of passengers.
Airport bosses have long wanted to up capacity with a third runway, and business groups have been broadly supportive. Pitched against them are numerous campaign groups who oppose the expansion on environmental grounds, and for the damage it would do to neighbouring villages.
Recently, the saga took a swing towards the pro-runway camp, when erstwhile Chancellor Rachel Reeves indicated that the Labour government was supportive of a third runway. Yet momentum now seems to be building in the opposite direction, with the Mayor of London, Transport for London and several local councils declaring their formal opposition.
Here, we take a brief look at the current status of the plans, as well as the pros and cons of Heathrow expansion.
Where would the runway go?
It would be slotted in north and somewhat west of the current airport footprint, covering much of the villages of Harmondsworth, Sipson and Longford. We've annotated the official graphic to help set the scene.
As well as a third runway, the expansion would also include a new terminal and (presumably) a rail link. A new tunnel would carry the M25 orbital motorway beneath the runway.
Heathrow's official expansion pages can be found here.
Why is it needed?
In two words: economic growth. In slightly more words, a bigger airport means more flights, means more connectivity, means more trade and more jobs, means economic growth. A third runway would also improve the airport's resilience to disruption. Without the third runway, argue business leaders, London could fall behind other large cities in Europe, as has now happened in the case of Istanbul.
What's the latest on the plans? Will this actually go ahead?
The airport bounced back strongly from Covid. The summer of 2024 saw record numbers of passengers using the airport (thanks Taylor Swift), and it is once again operating very close to capacity.
Meanwhile, the political stars seemed to be aligning. Labour were always stronger advocates of the third runway. When the party returned to power in 2024 with an urgent need to grow the economy, talk of expansion immediately bubbled up, with support from then-Chancellor Rachel Reeves.
Yet Mayor of London Sadiq Khan is not so keen. Tackling air pollution through policies like ULEZ is at the centre of his mayoralty, and he has been firmly against the expansion of Heathrow. The recent Draft London Plan (2026) maintains this stance: "Proposals for expansion at Heathrow and other airports should be refused unless no unacceptable environmental, transport, and congestion impacts are demonstrated." Even major airlines have voiced concerns that the project is too costly to be viable.
The airport, meanwhile, continues to make the economic case, saying that the project would create over 100,000 jobs across the country, and that it could be built with 100% private funding.
What are the downsides?
Heathrow will not find it easy to push through its plans. Numerous campaign groups and high-profile figures are opposed to any kind of expansion. The reasons are many.
- Hundreds of extra flights a day come with pretty obvious downsides. Noise pollution and fill-the-air-with-greenhouse-gas pollution would significantly increase.
- The construction phase will itself be environmentally damaging in terms of both emissions and loss of local wild habitat.
- The village of Longford would be totally destroyed. It contains seven listed buildings.
- About half of the village of Harmondsworth would be destroyed. Its magnificent Great Barn (described by Sir John Betjeman as the "Cathedral of Middlesex") and ancient church would be saved, but would be close up to the perimeter fence.
- Much of the village of Sipson would be destroyed by expansion, and the rest would be at the end of the runway.
- The village of Colnbrook to the west of the scheme would not be demolished, but it would find itself at the other end of the runway, with all the noise, pollution and safety fears that entails. This village contains around 30 listed buildings.
- In addition, five rivers would need to be concreted/bridged over and the Colne Valley Regional Park would be compromised.
- Harmondsworth Moor would be lost. As well as a valuable open space and nature refuge, the moor also contains dozens of fragments from the Old Waterloo Bridge, making it a unique historical curiosity.
- British Airways, obviously a key stakeholder in all this, would themselves be inconvenienced. Their huge Waterside office facility would have to be demolished. Two large immigration removal centres next door would also have to go.
Heathrow Airport's plans are keen to point out that "Significant community compensation schemes and impact mitigation measures" will be rolled out. But clearly, we're talking about smashing a medieval barn's-worth of eggs to make this particular omelette.
What are the alternatives?
Various alternatives to expansion have been mooted.
- Just don't do it, say opponents. Take the economic hit (the numbers are disputed anyway), because the price to the environment and the disruption to lives is not worth paying. We should be encouraging everyone to fly less, not more.
- Expand Heathrow's existing two runways to the west, then lop them in half to create four runways. This still has big down-sides, and does nothing to address environmental concerns, but it would at least save Longford, Harmondsworth and Sipson.
- Expand other airports, such as Gatwick, which would not require demolition of listed buildings and hundreds of homes, nor a costly tunnel for the M25. Plans are afoot to do this.
- Find other ways to expand capacity, such as bigger planes, increased efficiency or more night flights (itself controversial).
- Build a new airport in the Thames Estuary. A roundly mocked idea touted by Boris Johnson a decade ago.
- The giant aircraft carrier approach. Put all the infrastructure except for runways underground, freeing up room for two new runways parallel to the existing ones. Nobody has seriously suggested this... it is a madcap gedankenexperiment I put together back in 2013.
How did we get here? 12 key dates
2003: Publication of a White Paper recommending a third runway for Heathrow.
Nov 2007: Public consultation over plans for a third runway.
Jan 2009: Labour government announces support for expansion, with a tentative opening date of 2015.
May 2010: Expansion plans cancelled by the new Coalition government.
July 2015: The Airports Commission publishes a report calling for a new runway north-west of Heathrow.
Oct 2016: The Conservative government say that Heathrow will now be allowed to expand.
Jun 2018: The House of Commons votes overwhelmingly in favour of the third runway, with cross-party support.
Feb 2020: The Court of Appeal finds the plans to be illegal on environmental grounds. However, this is later overturned by the Supreme Court.
Jun 2019: The airport sets out its latest expansion plans for public consultation. Expansion would happen incrementally, cost £14 billion and take until 2050 to complete.
Mar 2020-2021: The Covid pandemic stalls the plans following the huge drop in passenger numbers. The recovery since has been swift and the stalled plans are now back on the table.
Jan 2025: Chancellor Rachel Reeves backs expansion, saying a third runway is "badly needed" and could create 100,000 jobs. She calls for proposals to be brought forward to summer 2025.
Jun 2026: The Government publishes the Draft Heathrow Expansion National Policy Statement, setting out the latest thinking and seeking views on the proposals. City Hall, Transport for London and many local councils responded in opposition to the plan.
