Heathrow Third Runway: £33bn M25 Tunnel Plan Puts Ancient Village of Harmondsworth at Risk

The UK government has thrown its weight behind Heathrow’s long‑debated third runway, choosing a £33 billion north‑west runway and M25 tunnel scheme that could wipe out much of the ancient village of Harmondsworth and neighbouring Longford. The decision, announced this week, sets up a new decade‑long struggle over climate targets, costs, and the fate of one of England’s most historic communities. ^[1]

What exactly has the government agreed to?

Ministers have selected Heathrow Airport Limited’s (HAL) “north‑west runway” as the preferred option for expansion and the basis for revisiving the Airports National Policy Statement (ANPS), the planning blueprint that underpins nationally significant infrastructure projects. It is not full planning permission, but it is the clearest political green light the project has received since the Supreme Court cleared earlier legal hurdles in 2020. ^[2]

Under the chosen plan, Heathrow would build a new 3.5km (2.2‑mile) runway to the north‑west of the existing airport. The runway would physically cross the M25, requiring a section of the UK’s busiest motorway to be diverted about 130 metres west and buried in a new tunnel beneath the expanded airfield. ^[3]

The government’s headline figure is around £33 billion for the new runway, a new terminal and the road realignment, within a wider £49 billion expansion and upgrade package at Heathrow. About £15 billion of that was already earmarked for modernisation works that will go ahead regardless, while £21 billion is attributed specifically to the runway itself and £12 billion to new and expanded terminal infrastructure. ^[4]

If built, the third runway would boost Heathrow’s capacity from roughly 84 million passengers a year to around 150 million, allowing up to 756,000 flights annually – roughly 760 more take‑offs and landings every day in the skies around London. ^[5]

Transport Secretary Heidi Alexander has argued that HAL’s proposal is the “most deliverable” option, capable of securing a development consent order by 2029 and opening the runway by around 2035, in line with Labour chancellor Rachel Reeves’s pledge to finally “end decades of uncertainty” over Heathrow’s expansion. ^[6]

A third runway that moves the M25

The most dramatic engineering element of the plan is its treatment of the M25. Instead of threading a shorter runway between existing roads, Heathrow will realign and widen the motorway between junctions 14 and 15, drop it into a tunnel and build the runway over the top. ^[7]

Estimates for this motorway work alone sit in the £1.25–£1.5 billion range, a vast civil‑engineering project in its own right. ^[8] Heathrow insists that most of the new carriageway would be built “offline” on adjacent land, with traffic switched over in a series of planned night‑time operations to reduce disruption. ^[9]

Critics are unconvinced. Local commentators warn that the scheme risks repeating the traffic chaos seen during previous upgrades at the nearby A3/M25 junction, potentially turning parts of Surrey and west London into regular bottlenecks for years. ^[10]

The ancient village in the firing line

Behind the high‑level engineering and cost debates lies a more intimate story: the future of Harmondsworth, the “ancient village facing ruin” that stands directly in the path of Heathrow’s preferred runway. ^[11]

Harmondsworth, just north of Heathrow, is a classic English village: a green framed by two pubs – the Five Bells and The Crown – and a parish church whose roots stretch back more than 900 years. Tucked behind the church is the Harmondsworth Great Barn, a vast Grade I‑listed timber structure built in 1426–27 and once described by poet John Betjeman as the “Cathedral of Middlesex”. ^[12]

The Great Barn is managed by English Heritage and occupies a special place in the national collection alongside sites such as Stonehenge and Hadrian’s Wall. Although earlier iterations of the runway plan kept the barn just outside the expanded airport boundary, English Heritage has repeatedly warned that a third runway would cause “irreparable harm” to its setting – surrounding a medieval masterpiece with tarmac, fencing and jet noise. ^[13]

The latest government‑backed scheme goes further: its footprint would require the demolition of large parts of Harmondsworth and neighbouring Longford, with hundreds of homes expected to face compulsory purchase. ^[14] Many residents have been living with the threat for more than a decade, a limbo extended by successive policy U‑turns, court cases and ministerial reviews.

Local reporting paints a community split between those who simply want the saga over – even if that means seeing their homes bulldozed in return for compensation – and those who feel they are being turned into collateral damage for national economic policy. Some residents told journalists this year that the runway would reduce their village to a “heritage shell”: a preserved church and barn, but without the living community that gives them meaning. ^[15]

How compensation for the Heathrow villages works

Heathrow’s existing compensation framework, developed under earlier iterations of the Airports National Policy Statement, offers affected homeowners a premium above normal compulsory purchase terms. Current policy documents describe offers of the “unaffected market value” of a property plus a 25% home‑loss payment, as well as covering stamp duty on a replacement home and reasonable legal and moving costs. For some zones, this translates into buyouts worth around 125% of an unblighted valuation. ^[16]

In practice, compensation is complex. Homeowners are split into categories, with more generous terms for long‑term resident owner‑occupiers than for landlords or recent buyers, and a discretionary hardship fund exists for people who need to sell before a final decision is made. ^[17]

For Harmondsworth and Longford, these schemes mean that if – and only if – the project secures development consent, many residents will be offered sums that are significant on paper but still cannot compensate for the loss of social ties, schools, places of worship and the physical fabric of their community.

Why Heathrow beat the rival Arora plan

Until this week, Heathrow’s north‑west runway was competing against a cheaper proposal put forward by hotel tycoon Surinder Arora’s consortium. The Arora Group offered a shorter runway – roughly 2.8km long and sited further east – which would have avoided moving the M25 and come with a claimed price tag of under £25 billion (before some costs). ^[18]

Ministers ultimately rejected that scheme. In a written statement and subsequent interviews, Alexander said Heathrow’s own design was more mature, had been stress‑tested in more detail and was judged the “most credible and deliverable option” to meet the government’s ambitious timetable for planning approval and a 2035 opening. ^[19]

Officials also argued that Arora’s shorter runway would still have required major works to the motorway network and, crucially, could have meant buying and demolishing even more homes. ^[20]

However, the government has stopped short of awarding Heathrow a total monopoly on delivering the infrastructure. Other companies will be able to compete to build the runway, terminals or associated works when the ANPS review is complete, opening the door for joint ventures or contractor‑led consortia to challenge Heathrow on price and design details. ^[21]

Economic case: growth, jobs – and big questions on cost

For Prime Minister Keir Starmer’s Labour government, backing the runway is part of a wider pitch that Britain must “build again” to unlock growth, even on politically difficult projects. Chancellor Rachel Reeves flagged Heathrow expansion as a priority in January, framing it as a way to secure new trade links, attract investment and show that the UK can still deliver megaprojects. ^[22]

Heathrow and supportive business groups talk about tens of thousands of new jobs during construction and up to or over 100,000 jobs in the wider economy once the expanded hub is fully operational. They argue that extra runway capacity will allow more long‑haul routes and restore domestic connections to UK cities that have lost direct flights as existing slots were reallocated to more profitable international services. ^[23]

But the price is eye‑watering. Regulators, airlines and campaigners all worry that a £49 billion upgrade bill – including £33 billion specifically linked to the expansion – will ultimately hit passengers through higher landing charges and ticket prices. ^[24]

International Airlines Group (owner of British Airways), Virgin Atlantic and others have already warned that Heathrow is one of the world’s most expensive hubs and that doubling charges to pay for the new runway could leave the extra capacity chronically underused. ^[25]

The Civil Aviation Authority has launched consultations on Heathrow’s regulatory model, and the government faces a delicate balancing act: it needs investors to back the project, airlines to keep flying, and voters to believe they are not being fleeced for vanity infrastructure. ^[26]

Climate, noise and the legal battles to come

Even if the numbers stack up, Heathrow’s third runway has to clear the UK’s increasingly stringent climate tests. The government’s latest position is that expansion can only proceed if it is compatible with legally binding net‑zero commitments and air‑quality rules – one of four “tests” covering emissions, noise, local air pollution and economic benefit. ^[27]

Environmental groups are adamant that this bar cannot be met. Friends of the Earth has described new aviation capacity as a reckless gamble with the climate, and long‑standing campaign coalitions promise to challenge every stage of the ANPS review and planning process. ^[28]

They point out that additional flights from Heathrow alone could add hundreds of millions of tonnes of CO₂ over the coming decades, undermining the UK’s broader decarbonisation efforts, and argue that technological fixes such as sustainable aviation fuel and more efficient aircraft are nowhere near ready to offset such a large capacity jump. ^[29]

The courts have already played a central role in Heathrow’s story. In 2020, the Court of Appeal ruled the government’s earlier expansion policy unlawful for failing to take the Paris Agreement into account. The Supreme Court later overturned that ruling, deciding that ministers had acted lawfully but making clear that up‑to‑date climate commitments would have to be considered again when a concrete planning application is examined. ^[30]

Local authorities around Heathrow – many of which have opposed expansion for years – are expected to pore over the updated ANPS and any development consent application in search of grounds for further legal challenge, particularly on noise, traffic and air‑quality impacts. ^[31]

Industry, unions and campaigners react

Reactions across west London and the aviation sector have been swift and polarised.

Business groups and some unions have broadly welcomed the decision, pointing to potential job creation in construction, engineering, logistics and tourism. Industry observers predict a surge in demand for specialist skills in tunnelling, major civils and airport systems if the scheme survives the planning gauntlet. ^[32]
Campaigners, including the No 3rd Runway Coalition, accuse ministers of backing an “absurdly expensive” plan that will burden travellers and the Treasury while destroying communities such as Harmondsworth for marginal economic gain. Some highlight the irony of a single airport car‑park in the plans being costed at more than an entire runway expansion at Gatwick. ^[33]
Local MPs in affected areas have renewed their opposition, arguing that constant aircraft noise, extra traffic and the loss of villages are too high a price for more slots to global business hubs. Others, particularly those focused on national growth, argue that the economic upside is too great to ignore. ^[34]

The split is mirrored within Harmondsworth itself. Some residents, exhausted by 20 years of uncertainty, told reporters they now support the Reeves plan on the basis that “if it’s going to happen, just get it done”, while neighbours remain determined to fight on. ^[35]

What happens next?

The decision to back Heathrow’s north‑west runway triggers a tightly choreographed but politically charged sequence of steps:

Airports National Policy Statement review – The government is revising the ANPS to reflect the new plan, with a full public consultation expected next summer and parliamentary scrutiny to follow. The updated statement will set the policy context against which any third‑runway planning application is judged. ^[36]
Development Consent Order application – Once the ANPS is updated, Heathrow (or another approved promoter) must apply for a DCO, triggering examination by the Planning Inspectorate, hearings on climate, noise and community impacts, and a final decision by the transport secretary. ^[37]
Regulatory and financing decisions – In parallel, the Civil Aviation Authority will refine the rules that determine how Heathrow can recover its costs through airport charges, while investors decide whether the numbers – and the political risk – add up. ^[38]
Construction phase – If consent is granted and financing secured, major enabling works on the M25 and surrounding roads would begin first, followed by runway and terminal construction. Heathrow and ministers currently talk about flights taking off from the third runway in 2035, but that timetable will depend on the outcome of legal challenges and market conditions. ^[39]

For travellers, little will change immediately; Heathrow will continue operating its two runways at full capacity for years to come. For villagers in Harmondsworth and Longford, however, the government’s latest move makes their long‑running dilemma more acute: stay and hope the project falters again, or prepare for a future in which their homes, pubs and streets are erased to make way for a longer runway and the buried roar of the M25.

Heathrow Expansion - The Preferred Masterplan