Mayor of London Boris Johnson has reduced the fundraising threshold that the Garden Bridge Trust has to reach before the bridge's future maintenance will be guaranteed by the taxpayer.
In June last year the Mayor agreed that the Greater London Authority would act as guarantor of the bridge's future upkeep if efforts to raise funds by the Garden Bridge Trust proved insufficient.
This guarantee was to be subject to "the trust demonstrating to the Mayor's satisfaction that it has secured a satisfactory level of funding to operate and maintain the Garden Bridge for at least the first five years from its completion".
After a decision signed by Boris Johnson on Friday – just two weeks before he leaves office – the guarantee is now merely subject to the trust having a "satisfactory funding strategy" but with no requirement to actually raise the cash in advance.
A City Hall report accompanying the decision admits that this is a "lower requirement" which "increases the risk that the guarantees will be called upon during the first five years after the bridge is completed".
The report – drafted by Greater London Authority head of governance and resilience Tom Middleton – concludes that "it is not realistic to expect the trust to have secured the income required for the first five years of maintenance ... prior to construction of the bridge itself having commenced".
Mr Johnson has previously insisted that the Garden Bridge's "maintenance costs will not be borne by the public sector".
The report by GLA officers also raises the possibility of City Hall taking ownership of the controversial bridge, noting that "in the event that any of the guarantees were called upon, the GLA would have the ability to take certain steps, e.g. to exercise its options to take overriding leases in respect of the Garden Bridge".
The GLA says that the gross annual operating and maintenance costs for the bridge are estimated to be in the region of £3 million, "although costs could be expected to be lower than this initially and to increase with the age of the structure".
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