There is no doubt that, long term, demand will continue to be strong and we are confident that traffic will double over the next 20 years

Mike Hodgkinson, chief executive BAA

The three London airports, Heathrow, Gatwick and Stansted, have four runways between them.

Luton, run by TBI plc, has another.

BAA chief executive Mike Hodgkinson said passenger numbers slumped after 11 September but demand is beginning slowly to pick up.

"There is no doubt that, long term, demand will continue to be strong and we are confident that traffic will double over the next 20 years.

"This investment is essential if Britain is to have the quality airports it needs."

Heathrow will see most of the planned investment with �2.7bn going on the new Terminal 5 - due to open in 2008.

The rest will go on Underground and rail extensions to the new terminal and improvements at the other terminals.

Rising demand

Gatwick in west Sussex is to get �980m for new extensions to its two terminals and for car park improvements.

Stansted in Essex, which opened a new terminal extension on Friday, is to get another �600m of improvements, including a new M11 slip road.

BAA predicts passenger numbers will grow sharply at the three airports.

Expected passenger numbers