The trust behind a project to build a bridge covered with trees and shrubs across the Thames in London has revealed it is “unable to conclude it is a going concern”.
The Garden Bridge Trust needs to raise an estimated £185m to complete the project.
But its latest annual accounts show a shortfall of £56m.
However, Garden Bridge Trust chair Lord Davies said trustees still expected construction to start this year.
The trust’s accounts for 2016 filed with Companies House show it has yet to secure the land on the South Bank of the Thames for the bridge’s southern landing.
They also show that the trust may need additional funding that would not be repayable “if the project is not able to proceed” in the first half of this year.
And the accounts raise the possibility that “in a worst-case scenario” the trust might have to consider “whether the project remains viable”.
If the project does not go ahead, London mayor Sadiq Khan has estimated that £40m of public money already spent would be lost to taxpayers.
In total the trust said it had received financial commitments totalling £129m from private investors, donors or public funds.
Of that, £60m is to come from the Department of Transport and Transport for London (TfL), £20m of which will be repaid to TfL by the trust over time.
But of the £39m raised in 2016 for the project, £26m came from the DfT, meaning the trust raised only £13m last year.
In the accounts, Lord Davies warns: “Due to material uncertainties in existence ahead of finalising these accounts trustees are unable to conclude that the trust is a going concern and feel it only appropriate to flag these risks.
“It is hoped that these will be resolved over the months ahead but since a number of these risks are outside of the control of the trustees, they recognised that if this is not possible they will need to consider the further delay to the project, and in a worst-case scenario, whether the project remains viable.”
The Garden Bridge has been beset with problems. In September Mr Khan ordered a review into whether the public had so far been given value for money from the project, adding he believed there had not “been the necessary standard of transparency and openness around the Garden Bridge”.
That review, led by Dame Margaret Hodge, a former chair of the House of Commons Public Accounts Committee, has yet to report back but Mr Khan has already said that no more taxpayer money will be provided to fund the project.
In October it emerged that former prime minister David Cameron had ignored the advice of civil servants over Garden Bridge funding, personally intervening to approve extra taxpayer money for the controversial project.
The National Audit Office (NOA) said at the time that nearly £23m of taxpayer money was at risk of being lost.