City Hall says that the taxpayer could lose £46.4 million if the Garden Bridge is not built, as Sadiq Khan formally revokes the decision by his predecessor Boris Johnson to underwrite the bridge's future maintenance costs.
In June 2015 Boris Johnson agreed in principle that London taxpayers would pick up the bill if the Garden Bridge Trust failed to raise enough money for the ongoing maintenance of the Garden Bridge.
In April 2016 – during his final weeks as Mayor of London – Mr Johnson reduced the fundraising threshold that the Garden Bridge Trust had to reach before the bridge's future maintenance would be guaranteed by the taxpayer.
At the end of April this year Sadiq Khan confirmed that he would not be providing the commitments to the Garden Bridge Trust pledged by his predecessor.
Sadiq Khan signed the mayoral decision notice on 9 May but the documents were not immediately made public due to the 'purdah' rules limiting the publication of new information by public authorities during the general election campaign.
In their advice to the Mayor, Greater London Authority officers note that "up to £46.4 million of public funds would be unrecoverable were the project to be cancelled".
The report prepared for Mr Khan by City Hall officials notes that "the risk of losing value from the existing public expenditure, however, is outweighed by the extent of the risks arising if the bridge continues with GLA guarantees".
Since Mr Khan pulled the plug on City Hall support for the project, the Garden Bridge has continued to enjoy the vocal support of the Evening Standard, including a recent opinion piece by architect Lord Rogers.