Buses don't have air conditioning, just windows. Normally these make a nice breeze when the bus is in motion, but London traffic is so congested that the buses there move too slowly to create a breeze.

Most London buses do not have traditional, heavy-duty air conditioning because the city's climate historically did not justify the high cost and fuel consumption associated with it. Until the 21st century, the UK rarely saw prolonged periods of extreme heat; however, as the number of days over 30°C has increased, Transport for London (TfL) has begun a multi-phase upgrade. Modern electric and hydrogen buses are now being built with more efficient "air cooling" or "forced-air ventilation" systems, which are lighter and more sustainable than traditional AC units. Additionally, many bus operators in 2026 have faced allegations of "disabling" air conditioning belts to save on fuel, though TfL officially denies this as a routine practice. The small, sliding windows on upper and lower decks are a relic of older bus designs intended to prevent passengers from falling out or throwing objects, which paradoxically often makes the interiors feel even more stifled on hot summer days.