Prime minister Gordon Brown has announced the government's financial backing for a railway linking east and west London but said businesses must also play their part in the project.
In a speech to business leaders this morning Mr Brown said the government has worked "day and night" during the past few months to achieve the financing necessary for the rail link to go ahead.
The government has already committed £400 million to detail design for the project; £16 billion is required in total.
Crossrail will connect the east, Canary Wharf and central London to Heathrow airport and to commuter areas east and west of the capital.
"A comprehensive package is needed to fund the £16 billion required - largely from the public sector but also including the proceeds from a supplementary business rate and additional contributions from certain London businesses and developers who will benefit significantly from Crossrail," the prime minister said.
"The City of London in particular will need to make a significant contribution.
"This is a huge national project that is vital for long-term prosperity of the nation's capital and indeed the whole country.
"And I can say today that if others are prepared to play their part, the necessary funding from the government will be provided in the forthcoming comprehensive spending review - funding only possible because we have kept public spending in other areas under control."
London mayor Ken Livingstone said "great progress" has been made on the project and welcomed the fact Crossrail is now within grasp.
"We will continue to work together to close the gap that still remains so that Crossrail can be announced together with the comprehensive spending review, and I am hopeful this can be achieved," he added.
If plans run to schedule then the main construction for Crossrail will begin in 2010 and the first trains will run from 2017.
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