The expansion of Heathrow Airport is a series of proposals to add to the runways at London's busiest airport beyond its two long runways which are intensively used to serve four terminals and a large cargo operation. The plans are those presented by Heathrow Airport Holdings and an independent proposal by Heathrow Hub with the main object of increasing capacity.
In early December 2006, the Department for Transport published a progress report on the strategy which confirmed the original vision of expanding the runways. In November 2007, the government started a public consultation on its proposal for a slightly shorter third runway () and a new passenger terminal.
The plan was publicly supported by many businesses, the aviation industry, the British Chambers of Commerce, the Confederation of British Industry, the Trades Union Congress and the then Labour government. It was publicly opposed by Conservative and Liberal Democrat parties as opposition parties and then as a coalition government, by Boris Johnson (then Mayor of London), many environmental, local advocacy groups and prominent individuals. Although the expansion was cancelled on 12 May 2010 by the new coalition government, the Airport Commission published its various-options comparative study "Final Report" on 1 July 2015 which preferred the plan.
On 25 October 2016, a new northwest runway and terminal was adopted as central Government policy. In late June 2018, the resultant National Policy Statement: Airports was debated and voted on by the House of Commons; the House voted 415–119 in favour of the third runway, within which outcome many local MPs, including a majority of those from London, opposed or abstained.
On 27 February 2020, in an application for judicial review brought by environmental campaigning groups, London councils, and the Mayor of London, Sadiq Khan, the Court of Appeal ruled that the government's decision to proceed with building the third runway were unlawful, as the government's commitments to combat climate change under the Paris Agreement were not taken into account. In response, the government announced it would not appeal against the decision, but Heathrow announced its intention to appeal to the Supreme Court.
On 16 December 2020, the UK Supreme Court lifted the ban on the third runway, allowing a planning application via a Development Consent Order to go ahead. The plan stalled in 2023 after post-COVID pandemic falling passenger numbers and concerns about investment costs, but as of June 2024 the third runway is still planned with a projected completion date around 2040. In January 2025, Chancellor of the Exchequer Rachel Reeves confirmed it was the new Labour government's plan to proceed with a third runway within the current parliamentary term.
Plans
2009 third runway and additional terminal plan
In January 2009, the then Transport Secretary Geoff Hoon announced that the UK government supported the expansion of Heathrow by building a third runway, long serving a new passenger terminal, a hub for public and private transport set apart from the Central hub between terminals 2 and 3, the southern hub of 4 and western hub of Terminal 5. The government would encourage the airport operator (BAA) to apply for planning permission and to carry out the work. The government anticipated that the new runway would be operational in 2015 or soon after. In 2009 the government stipulated it would limit extra flights to 125,000 per year until 2020, rather than the full capacity of circa 222,000. The third runway plans drafted involve compulsory acquisition and demolition of approximately 700 homes for which 125% market value would be paid to compensate families.
In January 2009, more detailed plans for a third runway were government backed subject to funding, legal and parliamentary approval, together with a terminal which would include a Heathrow Hub railway station to provide the first extra-London rail link using the Great Western Main Line, perhaps at the global definition of "high speed", involving the national High Speed 2 new railway project.
In March 2010, the route for High Speed 2 was announced. It did not include a direct connection with Heathrow, but did include a new station at Old Oak Common before reaching the London terminus of Paddington – also served by Crossrail.
On 12 May 2010, expansion was cancelled as part of the coalition agreement agreed by the new Conservative-Liberal Democrat government. BAA formally dropped its plans on 24 May 2010. However, London First, a lobby group representing many of London's businesses and major employers, continued to press the coalition government to rethink their opposition to the expansion of the airport.
On 1 July 2015, the Airports Commission recommended the third runway with further terminal, with a projected capacity (on completion) of 740,000 flights per year.
On 25 June 2018, the House of Commons voted 415–119 in favour of the third runway. The project received approval from most of the government. A judicial review of the decision was launched by four London boroughs affected by the expansion – Wandsworth, Richmond, Hillingdon and Hammersmith & Fulham – in partnership with Greenpeace and London mayor Sadiq Khan. Khan had previously said he would take legal action if it were passed by Parliament.
2013 Northwest runway plan In July 2013, the airport submitted three new proposals for expansion to the Airports Commission, which was established to review airport capacity in south-east England. The commission was chaired by Howard Davies who, at the time of his appointment was in the employ of GIC Private Limited and a member of its International Advisory Board. Since 2012, GIC Private Limited has been one of Heathrow's principal owners. Davies resigned these positions upon confirmation of his appointment to lead the Airports Commission, although it has been observed that he failed to identify these interests when invited to complete the commission's register of interests. Each of the three proposals that were to be considered by the Commission involved the construction of a third runway, to either the north, the north-west or the south-west of the current airport site.
The Commission released its interim report in December 2013. This shortlisted three options: the north-west third runway option at Heathrow extending an existing runway at Heathrow a second runway at Gatwick Airport
The full report was published on 1 June 2015; this confirmed the north-west runway and a new sixth terminal as the commission's chosen proposal. The Commission estimated the cost as around £18.6 billion; £4 billion higher than Heathrow's own estimate.
The north-west runway and terminal plan was approved by Government on 25 October 2016. In January 2018, in a public consultation, Heathrow unveiled another option with the new runway shorter, to reduce costs from £16.8 billion to £14.3 billion. This option would still require the M25 motorway to be diverted to a tunnel under the runway, west of its current route.
The financing of the expansion has yet to be arranged; Heathrow Airport Holdings' finances are already highly leveraged. In 2017 borrowings were £13.4 billion, with shareholder equity of only £0.7 billion.
2025 Labour government plans In January 2025, Chancellor Rachel Reeves confirmed that the Labour government would plan to proceed with the expansion of Heathrow Airport, saying it would "make Britain the world's best connected place to do business". London Mayor Sadiq Khan expressed his opposition on environmental grounds. The CEO of Heathrow Airport, Thomas Woldbye, said that an expansion was "urgent" as the airport was currently working at capacity, to the "detriment of trade and connectivity".
In June 2025, transport minister Heidi Alexander invited proposals which would deliver an operational third runway by 2035. Two responses were received: one from Heathrow Airport Holdings and a smaller-scale plan from Arora Group. In November 2025, Alexander announced that the government had adopted the scheme put forward by Heathrow Airport Holdings, the airport's owner. The proposal outlines a decade-long development centred around the construction of a third runway to be known as the north-western runway, which would be up to 3,500 metres (11,500 feet) in length. The proposal states this would increase the airport's annual capacity to 756,000 flights and 150 million passengers, up from the current figure of approximately 84 million passengers.
As well as the construction of a third runway, the plan includes:
A new terminal called T5X to be built, whilst expanding Terminal 2 and opening three new satellite terminals, with Terminal 3 to close. Enhancement of local rail connections, and walking and cycling routes. Realigning and widening the M25 between junctions 14 and 15, diverting it 130m to the west via a new road tunnel under the airport. Diverting several neighbouring roads including the A4 and A3044 around the north of the expanded airport boundary. Creation of two new Heathrow parkways. Improvements to Heathrow's bus and coach stations. Potential integration of the proposed Western Rail Approach to Heathrow and Heathrow Southern Railway.
The total estimated cost is £49 billion: £21 billion for the third runway (which includes procuring the land and altering the M25 motorway), £12 billion to build the new terminal, and £15 billion to modernise the airport's infrastructure. According to Heathrow, the expansion could contribute an additional 0.43% to UK GDP.
In September 2026, government sources told The Daily Telegraph that the 2035 target was unrealistic, and the current expectation was to obtain planning permission by 2029 and for the runway to become operational in 2039.
2025 Arora Group proposal A rival "Heathrow West" proposal was put forward in 2025 by the Arora Group, a large landowner in the area. It proposed a shorter runway of around 2,800m (9,200 ft) which would avoid rerouting the M25. Its total cost was estimated at approximately £25 billion. The proposal was rejected by the government in favour of the plans submitted by Heathrow Airport Limited.
Support Reasons for expansion The principal argument stated in favour of expanding Heathrow is to enhance the economic growth of the UK. As the UK's major hub airport, Heathrow can attract many transfer passengers, and so can support a wide range of direct flight destinations at high frequencies. In 2009 it was the world's second busiest airport, based on numbers of international passengers. The government stated in 2003 that Heathrow's connectivity helps London (and nearby counties) compete with other European cities for business investment, which in turn produces economic benefits for the rest of the UK. The transport secretary stated in 2009 that "additional capacity at Heathrow is critical to this country’s long term economic prosperity".
The government's argument in 2009 was that Heathrow was on the brink of suffering a decline in connectivity. Heathrow's runways were operating at around 99% capacity, which increases delays when flights are disrupted, and risks competing European airports gaining destinations (at Heathrow's loss). The government estimated that building a third runway would allow Heathrow to increase its connectivity, bringing £5.5bn of economic benefits over the period 2020–2080. However, the British Chambers of Commerce estimated the economic benefits to be £30 billion for the UK economy over the same timescale, and has also stated that every year the programme is delayed costs the UK between £900 million and £1.1 billion.