Heathrow’s £49bn expansion plan retains Grimshaw as lead architect
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Grimshaw has been retained as lead architect for Heathrow Airport’s £49 billion expansion, as the operator formally submitted proposals to the government for a third runway and extensive terminal upgrades. The plans, largely unchanged from those first made public in 2016, signal a significant escalation in both scale and cost, with the project now estimated at more than three times the £14 billion figure forecast in 2019.
The scheme, commissioned by Heathrow Airport Holdings, centres on a 3,500-metre runway positioned to the north-west of the existing site. The runway would cross the M25 motorway, which is slated to be widened and buried to address capacity issues at key junctions. Alongside the runway, Grimshaw’s design includes two new buildings linked to Rogers Stirk Harbour + Partners’ Terminal 5, a satellite terminal to the north, and an expanded Terminal 2 with a new satellite facility.
The submission follows a January announcement by Chancellor Rachel Reeves confirming government support for a third runway. The Department for Transport invited expansion bids from interested parties shortly thereafter, with a decision expected later this year.
Rival schemes and political backing
The Grimshaw-led proposal is not without competition. Arora Group, one of Heathrow’s largest landowners, has unveiled its own expansion plan, prepared by Scott Brownrigg, which features a shorter runway avoiding the M25 and a new terminal west of Terminal 5. Arora’s scheme remains the only rival concept to be made public, though Heathrow’s management has argued that no other proposal can meet the government’s target of having a third runway operational by 2035.
Heathrow’s leadership also notes that its scheme already benefits from the support of the Airports Commission and the Airports National Policy Statement, which have both endorsed the third-runway concept. The project has previously undergone judicial scrutiny, emerging with Supreme Court backing in 2020 after climate-related legal challenges were overturned.
Climate concerns and campaigner response
Environmental groups have voiced renewed opposition in the wake of the submission. Tony Bosworth, a climate campaigner at Friends of the Earth, questioned how the expansion could be reconciled with the UK’s legally binding climate targets.
“The UK’s green sector was the fastest-growing part of our economy last year,” Bosworth said. “The government must commit to a fully transparent and democratic decision-making process, consulting all interested parties. But, ultimately, it is hard to see how Heathrow expansion can go ahead without our legally binding climate targets being missed.”
Heathrow has maintained that the expansion can proceed in line with the UK’s net-zero commitments by 2050, positioning the project as a vital driver of capacity and economic growth in the long term.
Escalating costs and delivery timeline
The most striking change since the last public consultation in 2019 is the cost. At £49 billion, the price tag reflects updated construction estimates, logistical complexity, and the need for extensive enabling works. The M25 realignment alone is a major engineering undertaking, involving the burial of a motorway beneath the runway footprint and improvements at multiple junctions.
If the government backs Heathrow’s proposal, a final round of public consultation could take place in 2027, followed by a formal planning application by 2029. The airport would then seek a Development Consent Order to begin construction.
A pivotal decision for UK aviation
The expansion is framed by Heathrow as a necessary step to maintain the UK’s position as a global transport hub. The airport currently operates near full capacity, with passenger demand projected to rise sharply over the next decade. Proponents argue that a third runway would ease congestion, improve connectivity, and support growth in trade and tourism.
Opponents counter that the environmental cost is too high and that investment should instead focus on rail infrastructure and regional airport upgrades. The government’s decision, expected later this year, will determine whether Heathrow’s long-debated expansion finally moves forward after decades of political and legal wrangling.
With costs at record levels, public scrutiny intensifying, and climate commitments in play, the project now sits at the centre of a national debate over how the UK balances economic ambition with environmental responsibility.
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