Heathrow: What are the airport's expansion plans and why are they controversial?

27 January 2025, 16:52 | Updated: 29 January 2025, 12:12

Heathrow Airport's expansion plans could finally go ahead after almost 20 years of debates and delays.

Its potential revival comes after Chancellor Rachel Reeves indicated she would overrule environmental objections to allow London's biggest airport to carry out its plans in order to prioritise economic growth.

She has announced the government's support of a third runway - saying ministers "cannot duck the decision any longer".

Heathrow is the UK's busiest airport with more than 80 million travellers a year using its four passenger terminals and two runways.

But what exactly does the airport want to do, and why has it proved so controversial?

Heathrow wants a new runway

The west London hub wants to build a third runway to the north-west of the existing two, which it says would enable an additional 260,000 flights per year and "allow Britain as a sovereign nation to compete more effectively for trade".

Its plans also include a new terminal building to the west of Terminal 5 and the eventual demolition of Terminal 3 to make way for a series of new satellite terminals and more public transport.

Despite being given parliamentary approval in 2018, plans have been delayed by legal challenges and the COVID pandemic.

Why is it controversial?

Major works would be needed to build another runway at Heathrow.

The M25 would have to be rerouted and a new tunnel under a runway would have to be constructed.

Hundreds of homes would have to be demolished and rivers would need to be diverted.

There would be an average of 2,000 extra flights a day if another runway were built - the annual flight cap would lift from 480,000 to up to 720,000.

It could mean 140 million passengers using the airport annually.

Environmental groups have campaigned against the expansion since the plans were drawn up.

Jenny Bates, transport campaigner at Friends of the Earth, called the proposal for another runway at Heathrow "hugely irresponsible in the midst of a climate emergency", while Alethea Warrington, from climate charity Possible, said: "Approving airport expansions would be a catastrophic misstep for a government which claims to be a climate leader."

It has had critics across politics over the years, including from Labour's London mayor Sadiq Khan, on the basis of the impact on air quality, noise and net zero targets.

Boris Johnson was a long-standing opponent of the plans, and promised to "lie down in front of those bulldozers and stop construction" when he was London mayor for the Conservatives - though he toned down his rhetoric once he was prime minister.

One of the louder critics has been Ed Miliband, who threatened to resign from Gordon Brown's cabinet over the plans in 2009 when he was energy and climate change secretary.

In 2018, he said an expansion was "very likely" to make air pollution worse.

Mr Miliband, now net zero secretary, has said he will not resign from the government if the expansion goes ahead, adding that the government's position is for any aviation expansion to take place within the UK's carbon budgets, which are part of plans to meet the country's 2050 target of reducing emissions by 100% compared with 1990 levels.

"We believe that we can meet our growth mission - our number one priority - and keep within carbon budgets and indeed that our clean energy mission is crucial and a central part of meeting our growth mission," he said.

"Far from them being in contradiction, they are absolutely complimentary."

Other London airports also pushing for expansions

Gatwick and Luton airports are also hoping to expand in the near future.

Transport Secretary Heidi Alexander has a deadline of 27 February to make a decision on a second runway at Gatwick, which would effectively involve modifying an existing taxiway.

Gatwick's majority owners, VINCI Airports, said the £2.2bn project would create 14,000 jobs and generate £1bn a year in economic benefits.

But Communities Against Gatwick Noise and Emissions (CAGNE) insist they would legally challenge any second runway.

Meanwhile, Luton Airport, owned by the local council in Bedfordshire, has applied to build a new terminal and asked for permission to increase its passenger numbers to 32 million a year. It carried about 16.7 million in 2024.

Dr Alex Chapman, senior economist at the New Economics Foundation (NEF), said he believes the suggested growth benefits of UK airport expansion don't stack up.

He added: "The massive climate damage caused by these schemes will create deep physical and economic hardship for millions and will wipe out any benefit from the government's other climate policy efforts almost overnight."

What has Rachel Reeves said?

The chancellor has said that "by backing a third runway at Heathrow we can make Britain the world's best connected place to do business".

"That is what it takes to make decisions in the national interest and that is what I mean by going further and faster to kickstart economic growth," she added.

Ms Reeves said projects such as supporting the third runway "shows that this is a government with ambition that is getting on and delivering".

She added: "One of the reasons why we need to expand Heathrow is that there are emerging markets and new cities around the world that we aren't connected to because there aren't the slots at Heathrow - or indeed any other airport - to fly to."

The chancellor also dropped a heavy hint at the World Economic Forum in Davos, Switzerland, that she intends to dismiss climate concerns and back Heathrow, Gatwick and Luton expansion, saying "growth is the number one mission of this government".

Asked directly if she would now put the runway, along with expansion at Gatwick and Luton, ahead of the UK's net zero commitments, Ms Reeves said: "When the last government faced difficult decisions about whether to support infrastructure investment, the answer always seemed to be no.

"We can't carry on like that, because if we do, we will miss out on crucial investment here into Britain. You've already seen a number of decisions, including on Stansted and City Airport, on energy projects, on transport infrastructure because we are determined to grow the economy."

Conservative leader in favour of Heathrow expansion

Conservative Party leader Kemi Badenoch told Sky News' Sunday Morning with Trevor Phillips she "certainly would" back Heathrow's plans.

"I've had to vote on this before, and I voted in support of the third runway," said Ms Badenoch, whose North West Essex constituency includes London Stansted Airport.

"I know that it is very difficult for a lot of people when there's an airport in your area. I know, because I'm the MP for an airport as well. I have never opposed growth or development.

"What I want to do is make sure it's done in the right way."

Ms Badenoch added if the airport thinks it is able to deliver a third runway that meets all the criteria it has set, then we should "do the right thing".

"We are talking about the future," she said, adding: "I think that we need to make sure that we deliver infrastructure. I voted for it before, so why would I change my mind?"

Funding for Heathrow expansion could come from charging airlines more for using the airport, Heathrow's owner said.

Owners include Saudi Arabia and Qatar's sovereign wealth funds and private equity firm Ardian.

What has Heathrow said?

A spokesperson for Heathrow would not comment on reporting about a third runway, but said "growing the economy means adding capacity at the UK's hub airport which is full".

In a statement to Sky News, the airport added it was "looking at potential options to deliver a third runway at Heathrow in line with strict tests on carbon, noise and air quality".

(c) Sky News 2025: Heathrow: What are the airport's expansion plans and why are they controversial?