The project has been hampered by delays, pushing up the costs associated with the project.
Accounts filed on Companies House show that new funding for the bridge has not been found since 2015. However, the trustees still insisted construction will start in 2017 (the planning consents for the project expire in December).
The chairman of the trustees, Lord Mervyn Davies, said in a report on Companies House: "The project has been subject to a number of delays.
"This includes judicial reviews of local council decisions relating to the project, protracted negotiations with third parties and a changing political climate including a new mayor of London, the EU referendum and the subsequent change in government."
These delays meant that the final cost could "substantially" exceed the formal estimated cost of £185m, the report said. A new cost estimate for the bridge will not be available "until the hurdles have been overcome".
The bridge, which is supposed to provide a tree-lined pedestrian walkway across the Thames, has been partly funded by the public; £60m of its funding comes from the Department of Transport, of which £20m is a loan.
The trustees have also been batting off accusations that the accounts were filed late: