Ideas include lengthening platforms at dozens of stations and buying 1,500 carriages to create longer trains. More than 30 bottlenecks on the network could be removed by building flyovers to replace flat junctions and upgrading signals to reduce gaps between services.
Another idea is to combine the North, East and West London Lines with a new south London link to make an orbital railway by 2015.
London's population is expected to reach 7.9 million over the next decade, with tube and rail journeys expected to rise by 24 per cent. Another 600,000 passengers are predicted by 2025.