At his first Mayor's Question Time on Wednesday morning, Sadiq Khan has said it would cost more to cancel the Garden Bridge than to let it go ahead — so going ahead is what he's doing.
Khan's justification is that the Garden Bridge Trust has already spent £37.7m of taxpayers' money. (How? And on what?) That would all be lost if the project gets put on the scrapheap.
If it goes ahead, Khan says £20m of Transport for London's (TfL) money will be repaid as it's a loan. But the thing that tips the bridge into apparent viability is that it will pay £22m in VAT to the Treasury, presumably in construction costs etc.
It's not quite that simple, however. Citymetric calculated that loan could take up to 50 years to repay. Those are extremely generous terms, and means that TfL might get all its money back around the time it wants to start building Crossrail 5.
And that's before we get on to the issue of TfL underwriting maintenance costs — where Boris Johnson, in one of his last acts in office, lowered the bar for the Garden Bridge Trust to call on TfL to help it out. (In City Hall's own words: "this increases the risk that the guarantees will be called upon during the first five years after the bridge is completed.")
As for all the other potential issues with the bridge, we've outlined them with increasing weariness over here.