Plans for a third runway at Heathrow Airport face renewed uncertainty following private objections from Prime Minister Andy Burnham, who has expressed long-standing opposition to the project. Although the Labour government announced support for Heathrow’s expansion in early 2025, the prime minister’s stance appears less definitive behind closed doors, raising questions about the future of the development.

Burnham, who assumed office in July, reportedly conveyed to MPs that he has never favored the scheme but has yet to indicate his current position publicly. A Labour source described Burnham as "open-minded," suggesting he is awaiting the findings of a Transport Select Committee report before making a final decision. The committee is currently scrutinizing the government’s draft “Heathrow Expansion National Policy Statement” (HENPS), published in June, which outlines the case for increased airport capacity and the criteria required for development consent.

The Heathrow expansion project has been politically contentious for over two decades, alternating between support and resistance. It was initially paused by Heathrow’s management before being revived last year by then-Chancellor Rachel Reeves as a driver of economic growth. Her successor, John Healey, indicated in January 2025 that the government had given the go-ahead to the project, emphasizing its potential contribution to economic development. However, officials caution that this does not amount to an unconditional endorsement from Burnham’s administration.

Burnham, formerly mayor of Greater Manchester, criticized the Heathrow expansion last year, arguing that it diverts infrastructure investment from the North to London and the South East and fuels an overheated economy, contrary to efforts to promote regional balance. Despite his objections, some London Labour MPs and affiliated trade unions remain strong supporters. Dame Siobhain McDonagh, MP for Mitcham and Morden, described the runway expansion as beneficial for jobs, apprenticeships, and local communities, calling for the project to move forward after protracted debate.

Environmental concerns also complicate the project’s prospects. The independent Climate Change Committee recently warned that Heathrow’s expansion conflicts with the government’s climate goals, estimating the additional emissions could equal those of the city of Birmingham. This environmental challenge intersects with broader policy tensions, as the prime minister faces difficult decisions over permitting North Sea oil and gas projects simultaneously with airport expansion, given strict national carbon budgets.

Airlines such as British Airways and Virgin Atlantic have expressed apprehension about the project’s escalating costs, which currently stand at a £33 billion estimate. They warn that higher passenger charges could reduce Heathrow’s competitiveness against European rivals like Amsterdam’s Schiphol Airport. Additionally, London Mayor Sadiq Khan released a formal response to the government consultation criticizing the plan’s potential negative impacts on air quality, noise pollution, and transport infrastructure.

Heathrow officials are awaiting clearer guidance from the prime minister, particularly with the upcoming Budget expected to signal future government priorities. Downing Street declined to comment on Burnham’s private opposition, while a Heathrow spokesperson emphasized the project’s capacity to generate jobs and economic growth without imposing costs on taxpayers. The final government position on the third runway remains forthcoming as political, environmental, and economic considerations continue to converge.