Ministers are preparing to step in with hundreds of millions of pounds of public money to prevent the collapse of the £1.45bn scheme to widen the M25.
ConnectPlus, the preferred bidder for the scheme, is in talks with 20 banks to secure private finance initiative (PFI) funding for the project, which is due for completion before the 2012 Olympics.
But while all are understood to have given their nominal agreement to the project, most are awaiting approval from their internal credit committees, with some expected to withdraw.
As a result, the government is preparing to underwrite the scheme, as its financing has been delayed by the credit crunch.
The wrangling underlines problems the government faces in increasing infrastructure spending to give a Keynesian boost to the economy, with the number of PFI schemes signed off last year falling sharply.