The long‑debated expansion of Heathrow Airport has taken a decisive step forward, with the UK government formally backing the airport’s preferred proposal for a third runway — a £49 billion scheme that includes rerouting the M25 motorway into a new tunnel beneath the expanded airfield. The plan, described by ministers as the “most credible and deliverable option,” aims to significantly boost airport capacity, improve transport connectivity, and reinforce the UK’s position as a global aviation hub.
However, the project continues to face strong environmental and community opposition, with concerns centred on noise, air pollution, and the climate impact of increased flight numbers.
A Transformational Infrastructure Programme
Heathrow’s preferred expansion plan includes several major engineering components:
M25 Tunnel Diversion
One of the most complex elements involves diverting the M25 — one of Europe’s busiest motorways — into a new tunnel that would run beneath the proposed runway. The motorway would be shifted approximately 130 metres west of its current alignment to maintain traffic flow during construction.
New 3.5 km Runway
The centrepiece of the expansion is a 3,500‑metre (2.2‑mile) northwest runway, enabling Heathrow to increase annual flight movements from 480,000 to as many as 756,000 — an uplift of around 276,000 flights per year.
Terminals and Transport Links
The wider programme includes:
• New and expanded terminal facilities
• Upgraded rail connections
• Enhanced transport hubs to support increased passenger volumes
These improvements are designed to future‑proof Heathrow’s role as the UK’s primary international gateway.
Timeline and Delivery
Heathrow’s masterplan suggests that the new runway could be operational by 2026, with full project completion stretching to 2050. However, this remains subject to final planning approvals, environmental assessments, and the outcome of ongoing policy reviews. The expansion now forms part of the government’s review of the Airports National Policy Statement (ANPS), with further public consultations expected in the coming years.
Support and Opposition
Supporters
Proponents — including business groups and government ministers — argue that the expansion will:
• Strengthen UK trade links
• Boost tourism
• Create thousands of jobs
• Enhance long‑term economic competitiveness
Transport Secretary Heidi Alexander has repeatedly described Heathrow’s proposal as the “most credible and deliverable option” compared with alternative schemes.
Opponents
Environmental organisations, local residents, and London’s Mayor remain firmly opposed. Their concerns include:
• Increased aircraft noise
• Higher levels of air pollution
• Significant climate impacts from additional flights
Campaigners argue that expanding Heathrow undermines the UK’s climate commitments and will worsen quality of life for communities under flight paths.
What Happens Next?
The government’s backing does not mean construction will begin immediately. Key next steps include:
• Completion of the ANPS review
• Further environmental scrutiny
• Statutory public consultations
• A Development Consent Order (DCO) application by Heathrow
Final planning decisions are expected over the coming years, meaning the project still faces political, legal, and environmental hurdles before any tunnelling or runway construction can begin.
Sources
Parliament News – Heathrow third runway approved, M25 relocation
Metro – Inside Heathrow’s £49bn third runway plan
The Independent – Ministers back Heathrow’s plan to move M25
Yahoo News UK – Heathrow reveals plan for new runway and M25 tunnel
