Heathrow expansion: third runway, T5X, and the 2026 decisions that matter

The phrase "Heathrow expansion" covers four threads running in parallel. First, the third runway: a 3,500-metre new runway proposed to the north-west of the existing airfield, with the M25 motorway realigned to run beneath it. Second, a new terminal complex (Heathrow's proposal calls it T5X) to the west of Terminal 5, sized to add the capacity the new runway makes possible. Third, the modernisation thread: an expansion of Terminal 2 with two new satellite piers and the phased closure of Terminal 3, freeing the Central Terminal Area for redevelopment. Fourth, the regulatory and policy thread: the Airports National Policy Statement review running through 2026, the Civil Aviation Authority's decisions on what the airport can charge airlines, and the Parliamentary vote in the autumn that sets the formal planning framework.

As of May 2026 none of this is yet under construction. The third runway is a proposal, not an approved project. The government has chosen Heathrow Airport Limited's scheme as the preferred basis for the ANPS review, but the final ANPS still has to pass parliament. A rival scheme backed by major airlines remains in play. The first flights from any new runway are at least a decade away and probably longer. The honest reading of the project is not "approved" and not "cancelled"; it is "in process", with the next twelve months carrying the decisions that matter most.

The project has been here before. Labour government approval in 2009. Cancellation by the incoming Coalition government in 2010. The Davies Commission backing Heathrow in 2015. Parliament voting through the Airports National Policy Statement in June 2018 with cross-party support. The Court of Appeal ruling that ANPS unlawful in February 2020 on climate grounds; the Supreme Court reinstating it in December 2020. A pandemic that paused everything. Across all of that, no spade in the ground.

The 2025 reset is the clearest shift in over a decade. In January 2025 Chancellor Rachel Reeves confirmed the Labour government's support for expansion, calling a third runway "badly needed" and citing Heathrow's own forecast of 100,000 jobs. The government called for proposals by summer 2025. In August 2025 Heathrow submitted its £49 billion shovel-ready scheme. On 22 October 2025 the Transport Secretary formally commenced the ANPS review. On 25 November 2025 the government picked Heathrow's scheme as the preferred basis for that review, choosing it over the rival Heathrow West proposal from the Arora Group. In April 2026 the CAA published its draft decision on early cost recovery. The 2026 milestone schedule is now set out below.

Heathrow Airport Limited's August 2025 submission is the government's preferred basis for expansion. The headline numbers, all from Heathrow's own filings:

• £21 billion for the new runway and airfield infrastructure, including the M25 realignment.
• £12 billion for new terminal and stand capacity. The new terminal complex is called T5X, sited to the west of the existing Terminal 5, with an associated airside satellite called T5XN linked to the new runway.
• £15 billion for modernising the existing terminals, including the expansion of Terminal 2 with two new satellite piers and the phased closure of Terminal 3.

The runway is a 3,500-metre north-west runway, sized for any current commercial aircraft. The M25 between junctions 14 and 15 is realigned beneath the runway, in tunnel; this is the single most expensive piece of infrastructure in the scheme and one of the main reasons the headline cost is what it is. Capacity rises from around 84 million passengers a year today to a target 150 million, with up to 756,000 flights a year. The capital is described as 100% private, funded by Heathrow's shareholders and repaid through regulated airline fees over decades.

For the terminal infrastructure, T5X is positioned as a second front door to the existing T5 building, roughly similar in size, with a shared public transport interchange and public space between the two. The airside satellite T5XN sits closer to the new runway. The £15 billion modernisation thread expands Terminal 2 with two new satellite piers and phases out Terminal 3 once the new capacity is online. For the precedent of what a Heathrow satellite expansion looks like in practice, the recent build-out is on the T5B and T5C satellites. The full picture of how the existing terminals fit together is on the terminals overview.

The 100,000 jobs figure that appeared in both the Chancellor's January 2025 statement and Heathrow's own materials is Heathrow's forecast, not an independent economic projection. Read it as the airport's case for the project, not as a guaranteed outcome.

Heathrow West is the rival scheme from the Arora Group, the property and hotel business owned by Surinder Arora. The full corporate vehicle is Heathrow West Limited. The technical design partner is Bechtel, the US engineering firm. The headline differences from Heathrow's own plan:

• Phased runway. The initial runway is 2,400 metres, extendable to a full length later as demand justifies. The shorter phase-one length avoids the costly M25 realignment.
• Terminal 6. A new terminal sited to the west of Terminal 5, designed to handle up to 40 million passengers a year.
• Lower headline cost at the phase-one stage, with the full-length runway and onward capacity layered on later.
• 2035 phase-one operational target, in line with the government's stated timetable.

The scheme is backed by IAG (the parent of British Airways, Iberia, Aer Lingus, and Vueling, the airline group with the largest Heathrow operation), Virgin Atlantic, IATA, the Heathrow Airline Operators' Committee, and Swissport. IAG chief executive Luis Gallego has called the two-phase approach "a credible option" that "should be carefully considered". Virgin Atlantic chief executive Corneel Koster has said the scheme "is credible and should be considered by UK Government as a viable option". An updated concept was published on 18 May 2026.

The government did not pick Heathrow West as the preferred scheme in its 25 November 2025 decision; the preferred basis for the ANPS review is Heathrow's own £49 billion plan. Heathrow West remains under active consideration. The CAA's April 2026 draft decision allowed Heathrow West Limited to recover £4.3 million of its early development costs alongside the £320 million for Heathrow Airport Limited. The Arora Group has confirmed it intends to submit a Development Consent Order application for Heathrow West in November 2027, regardless of whether the government changes its preferred-scheme position. Read the two schemes as live alternatives, not as one approved plan and one campaign.

The pattern that the timeline shows is the one worth holding in mind: the project has been backed and unbacked many times across two decades, and every previous "approved" milestone has been delayed, cancelled, or overturned. The 2026 ANPS vote is the next decision point of the same kind. Approval in autumn 2026 puts a third runway on a path to planning permission by 2029 and first flights by the mid-2030s. Refusal, or a court challenge that succeeds, resets the project again.

Four scheduled decision points in 2026 shape what happens next. Each one has its own venue and process.

• Spring and summer 2026: Civil Aviation Authority cost recovery. The CAA published a draft decision in April 2026 allowing Heathrow Airport Limited to recover £320 million of early planning and design costs across 2025 and 2026, plus £4.3 million for Heathrow West Limited up to the November 2025 government decision. The CAA consultation runs to 15 June 2026, with a high-level outcome in July and the final decision later in the summer.
• Summer 2026: CAA regulatory model. A separate CAA decision sets the long-term price control framework under which Heathrow can charge airlines and recover the capital cost of construction. This is the framework that underpins the "privately funded" framing of the project.
• Summer 2026: draft Airports National Policy Statement. The Department for Transport publishes the draft updated ANPS, the document that sets the planning framework for a third runway. Public consultation and parliamentary scrutiny follow.
• Autumn 2026: Parliament votes on the final ANPS. The vote sets the formal policy framework. A successful vote puts the UK on course for first flights from a third runway within the following decade, per the government's own framing. A defeated vote or a successful judicial challenge resets the policy clock.

The decisions are sequenced rather than parallel: each one feeds into the next. The CAA work is about money; the DfT work is about policy; the parliament vote is about the policy framework as a whole. Heathrow's own Development Consent Order application sits later, targeted for 2027, with the planning permission target a further two years after that.

The shortest credible answer to "when will the third runway open" is 2035, and even that assumes everything stays on track. Heathrow's own framing is "first flights within a decade" of approval. With ANPS approval in autumn 2026, planning permission in 2029, and a four to seven year build, the earliest realistic operational date is 2035, with the late 2030s more likely once delays are factored in.

The project has slipped before. The 2009 Labour approval did not survive the 2010 change of government. The 2018 ANPS was challenged in court, ruled unlawful in February 2020, then reinstated by the Supreme Court in December the same year. Planning permission can be challenged. Construction can encounter ground conditions, archaeological finds, or supply-chain disruption that pushes timelines. The full project, including the modernisation of the existing terminals and the eventual closure of Terminal 3, runs over decades, not years.

The Heathrow West rival scheme targets phase-one operational by 2035 with its shorter initial runway. Even on the rival's faster framing, the timeline lands in the same decade.

Heathrow's expansion capital is private; the airport is owned by an international group of pension funds and sovereign wealth funds rather than the UK government. But "privately funded" needs qualification. The investment is repaid over decades through the airport's regulated revenue, which is dominated by airline fees. Airlines pass those fees on to passengers in ticket prices. So in practice, the cost of expansion is paid by the people flying through Heathrow over the lifetime of the project.

The CAA sets the price control framework that governs how much Heathrow can charge airlines. The H7 framework, currently in effect, runs through to the next regulatory period. The April 2026 draft decision allows Heathrow Airport Limited to recover £320 million of early planning costs across 2025 and 2026, plus £4.3 million for Heathrow West Limited. The Financial Times has estimated the per-passenger impact of the £320 million figure at about 10p. That is the early-cost number; the full project cost recovery scales up substantially as construction begins.

The 10p estimate is for the planning-phase cost recovery only. As the build phase begins, the CAA's price control will set the rate at which Heathrow can recover the full £49 billion (or the equivalent Heathrow West figure), and the per-passenger cost will rise accordingly. The exact path depends on the CAA's summer 2026 long-term regulatory model decision.

Opposition to a third runway is real, organised, and persistent. The 2020 judicial review that briefly killed the project off was brought jointly by the Mayor of London, four London boroughs (Wandsworth, Richmond, Hillingdon, and Hammersmith & Fulham), and Greenpeace, on climate grounds. In the 2025 reset, the same broad coalition has reformed.

Sadiq Khan, the Mayor of London, has publicly opposed the expansion and threatened legal action against any new approval. Hillingdon Council (Conservative-led), Wandsworth (Labour), Richmond (Liberal Democrat), Kingston, and Windsor and Maidenhead councils have signalled coordinated opposition. The No 3rd Runway Coalition is the main civil-society campaigning vehicle. Ruth Cadbury, the Labour MP and chair of the Commons transport committee, has been a vocal Labour critic. Dale Vince, the renewables entrepreneur and Labour donor, has publicly opposed Reeves's January 2025 backing.

The grounds for opposition cluster around three themes: noise affecting residential areas under the new flight path, air quality in west London, and climate impact at a time of net-zero commitments. The environmental case is the one that ended the project in February 2020 and is again the strongest live tension in the 2026 ANPS review. The Supreme Court's December 2020 reversal turned on a specific reading of how climate obligations entered the original ANPS, and the same question will likely return in any 2026 challenge.

Two pieces of terminal-side work are already part of the wider expansion thread, separate from the third runway itself. Both sit inside the £15 billion modernisation strand of Heathrow's own plan.

Terminal 1 demolition. Terminal 1 closed to passengers on 29 June 2015 and stood largely empty for a decade, used for baggage operations and emergency training. In 2025 Heathrow announced demolition plans to free the site for the eastern expansion of Terminal 2. The demolition has been signalled but not all of the building has yet come down at the time of writing.

Terminal 2 expansion and the planned Terminal 3 closure. The same £15 billion modernisation thread adds two new satellite piers to Terminal 2 and phases out Terminal 3 once the new capacity is online. The satellite-pier expansion is the same architectural template as the existing T5B and T5C satellites at Terminal 5, which remain the closest editorial precedent for what the new Heathrow terminal capacity will look like. T3 is the oldest building in current use at Heathrow (originally opened in November 1961) and is the natural candidate for closure once T2 capacity replaces it.

The terminal-side work is dependent on the runway scheme passing the 2026 milestones, because the T5X capacity that absorbs the eventual T3 closure is part of the same plan. But the T2 expansion and the T1 site clearance can move ahead independently in the interim.

The practical answer for a passenger flying through Heathrow in 2026: not much, yet. All four operating terminals stay open and operating throughout the decision and construction phases. Terminal 2, Terminal 3, Terminal 4, and Terminal 5 continue as they are. The four rail services into the airport (Heathrow Express, the Elizabeth Line, the Piccadilly Line, and the long-distance coach network) operate unchanged.

The one thing that does affect passengers in 2026 is the airport fee. The CAA's draft decision allowing Heathrow to recover early expansion costs adds a small amount to ticket prices, estimated by the Financial Times at about 10p per passenger from the £320 million already approved. The figure will rise gradually as the project moves from planning into construction, but no large step-change is scheduled in the next year. The full price-control framework that sets the longer-term path lands in the summer 2026 CAA decision.