Comment: A long struggle but it will change London forever

It has taken a very long time to deliver the Parliamentary planning powers needed to build Crossrail. In its modern form, the project was first proposed in 1989. Since then, it has been suspected that first the Conservative government and now a Labour one liked the idea of building the line but could not bring itself to pay up.

Last autumn, Gordon Brown held a meeting with transport chiefs to provide a physical expression of his desire to push on. The money is expected to come in broadly equal chunks from the Treasury, a levy on business ratepayers and borrowing against future fare income. The City of London is also expected to get big companies to make one-off contributions. The process of putting together the £16 billion required is still in progress. Until then, even Parliamentary powers will not be sufficient to ensure the Queen can be booked to start the digging.

Crossrail is supposed to open for business in 2017. This means that the years from 2009 to 2012 will require the funding of three huge projects in parallel. Not only will Crossrail start, but the Olympics will reach its most expensive stage, while the Tube PPP comes up for re-pricing. At a time when the Treasury is weak and strapped for cash, it is hard to see how extra resources will be found.

When the project is complete, an extra 24 national rail-sized trains per hour will cross central London, connecting Maidenhead and Ealing with Stratford and Brentwood via Bond Street and Tottenham Court Road. It will change London forever, opening up the East End to massive redevelopment and adding to development pressures in the West End and the City.

London needs Crossrail. The population is projected to grow to eight and then nine million by the 2030s. New transport infrastructure is essential if the city is to remain a good place to live and do business. Once the new line is started, lobbying for the next route - previously known as the Chelsea-Hackney line - must commence. Given the time it has taken to get this far with Crossrail, time is of the essence.

Tony Travers is director of the Greater London Group at the London School of Economics.