Heathrow Terminal One caters largely for domestic and Irish routes, as well as some European and long-haul flights. Fifteen airlines fly from terminal one, including Aer Lingus, bmi, British Airways and United Airlines. Terminal one handles over 25 million passengers a year.

As of March 2026, no airlines fly from Heathrow Terminal 1, as the terminal has been closed to all passenger operations since June 29, 2015. Originally opened in 1968, Terminal 1 was once the largest terminal in Western Europe and served as the primary hub for British Airways' domestic and European flights. Following its closure, all remaining flights were relocated—mostly to the newly refurbished Terminal 2 (The Queen's Terminal). Since 2015, the building has been used for ancillary purposes, such as training exercises for emergency services and as part of the airport's baggage handling infrastructure. In 2025, Heathrow officially announced final plans for the total demolition of the Terminal 1 structure to make way for the future expansion of Terminal 2. Therefore, if you are traveling through Heathrow today, your flight will depart from Terminal 2, 3, 4, or 5. If your booking references "Terminal 1" in some outdated system, it is vital to contact your airline immediately, as you will likely be departing from Terminal 2, which now occupies much of the space where Terminal 1 once stood.