Heathrow Airport has formally submitted detailed plans for a third runway as part of a proposed £49bn (€56.5bn) infrastructure expansion. The government claims the project could deliver major economic benefits – including the creation of 100,000 jobs – and boost the UK’s status as a global transport hub.

The proposed 3.5km runway, which would require rerouting part of the M25 motorway, is projected to support more than 750 additional daily flights and increase Heathrow’s annual passenger capacity to 150 million. Airport officials say the scheme is “shovel-ready” and aim to have the runway operational within the next decade. They argue that it would unlock at least 30 new international routes.

However, London mayor Sadiq Khan remains a vocal skeptic of the expansion, despite acknowledging aviation’s contribution to the economy. Following the submission of the runway plans, Khan said he “remain[s] unconvinced that you can have a new runway at Heathrow, delivering hundreds of thousands of additional flights every year, without a hugely detrimental impact on our environment.”

“City Hall will carefully scrutinise the new Heathrow expansion proposals – including the impact these would have on people living in the area and the huge knock-on effects for our transport infrastructure, which would require a comprehensive and costed plan to manage. I’ll be keeping all options on the table in how we respond.”

In a recent interview, Monocle asked Khan whether Heathrow’s proposed growth could spark conflict with central government, particularly as national leaders push for accelerated infrastructure development and increased air-travel capacity:

“Aviation is important for our economy but I support a better Heathrow, not a bigger one,” he told Monocle’s editor in chief, Andrew Tuck. “The noise pollution already affects more people than all major European hubs combined – and that’s with just two runways.”

“Air quality around the airport is still poor and a third runway would only worsen it. Plus, the Climate Change Committee says that aviation growth must meet carbon goals. Can Heathrow do that?”

“Then there’s the infrastructure; rerouting the M25, tunnelling, upgrading the Piccadilly line, the Southern Rail and the Elizabeth line. It’s not the best use of money. Though I agree with the government on most issues, on this, maybe not.” 

As the project moves into the planning approval phase, it’s clear that the debate over Heathrow’s third runway is far from over and might become a defining test of the UK’s infrastructure priorities in the face of climate and public health concerns.

Read Monocle’s full interview with Sadiq Khan here.