Gatwick has called for a re-think on runway capacity after recording its busiest July.
The airport reported 4.3 million passengers travelled through last month, a 6.4% increase on last year.
An additional 260,000 passengers used the airport compared with the same month in 2014, mainly due to an increase in long-haul flights and larger aircraft.
Consecutive month-on-month growth at the airport has continued for the past 30 months, with demand for long-haul flights to New York, Los Angeles, Cape Verde, Trinidad and Costa Rica contributing to increased passenger numbers.
The rise proves a new runway is needed and the Airports Commission should re-think its decision to support a third runway at Heathrow over Gatwick, chief executive Stewart Wingate said.
He said: "These results put us 10 years ahead of the forecasts used by the Airports Commission to predict future air traffic movements.
"Our growth in the last 12 months is actually more than the Commission concluded could be added at Gatwick in the first year of a new runway.
"This is further proof of the flaws in the Airports Commission analysis and shows its conclusions are fast unraveling."
In June, Gatwick reported its busiest year in history.
