BAA has announced an €13bn investment programme at London's three main airports.
The 10-year programme - some of which will need planning permission - assumes air traffic will double over the next 20 years.
BAA chief executive Mike Hodgkinson says: "The investment is essential if Britain is to have the quality airports it needs."
The plan does not take into account any extra runways that could be built in south-east England.
Government options for airport and runway capacity are to be published shortly, to be followed by an aviation White Paper which is expected to contain firm policy.
At Stansted, BAA hopes to invest a further €260m in extending the terminal further to take the airport's capacity to 26.3 million passengers a year by 2012-13 and, eventually, up to 35 million.
Passenger numbers at Heathrow, Gatwick and Stansted are forecast to grow from 104.9 million in 2001-2 to 153 million in 2012-13, with 84.7 million passengers using Heathrow alone by then.
This is an increase for the three airports of 45.8%, and the forecast average annual increase is 3.5%.