Heathrow Airport has formally submitted plans to build a third runway and expand its capacity to handle up to 150 million passengers annually, up from the current 84 million. The proposed £21bn runway, part of a wider £49bn redevelopment, would be constructed within the next decade and include a new terminal complex, with extensions to Terminal 2 and the demolition of older terminals. The expansion has government backing but faces strong opposition from local officials, environmental groups, and residents, who cite concerns over pollution, noise, and community impact. Rival proposals and debates over funding, passenger charges, and environmental claims continue as the government prepares to review all options later this year.