Heathrow’s bid for a third runway has entered a political minefield as the likelihood of Chancellor Rachel Reeves leaving office after the May local elections climbs. The airport must lock in formal planning consent before 2029 to start construction, a timetable industry insiders deem overly aggressive. Reeves revived the scheme in January 2025 and has been its most vocal champion.

If Reeves departs, sources close to Heathrow say the project could stall. Energy Secretary Ed Miliband, a long‑time opponent, is tipped to replace both Prime Minister Keir Starmer and the chancellor if Labour loses heavily on May 7. A postponement would give the next general‑election winner, due by 2029, a clear opening to scrap the scheme, while Greens and Liberal Democrats stay firmly opposed.

Heathrow argues any chancellor will back the expansion, claiming it would lift UK GDP by 0.5 percent. Unions such as the Community union, representing steelworkers, publicly praised Reeves for championing the runway. With Reform UK promising emergency legislation and the Conservatives still supportive, the airport’s fate now hinges on whether political turbulence can be insulated from a project that promises modest economic gain.