The bridge, which is backed by actress Joanna Lumley, is due to receive £60m of public funding including £30m from Transport for London which is chaired by Mr Johnson.
As part of their planning consent Westminster and Lambeth councils sought guarantees that the City Hall would underwrite the the bridge’s maintenance costs should the trust building it be unable to meet its obligations.
The Mayor repeatedly insisted he would not agree to these demands, and in December told London Assembly Members: “I can confirm that no such agreement has been made, nor will I make any such undertaking to do so.”
He later told LBC that the costs “will not be borne by the public sector”.
However on Thursday Mr Johnson signed a formal Mayoral Decision agreeing to underwrite the costs in order to allow the project to go-ahead.
Figures provided to City Hall by the trust suggest it will receive £3m per year “from retail, events, merchandise, ongoing fundraising, a patrons’ scheme, corporate memberships and an endowment fund.”
The estimated annual operating and maintenance costs are estimated at £1.975m, creating a claimed surplus of £1.025m each year.
The Mayoral Decision states “it is the clear expectation that the guarantees described above will not need to be called upon” because “income will exceed costs for the life of the bridge.”
Johnson’s decision to underwrite the costs comes a day after a majority of London Assembly members backed a motion calling for TfL’s contribution to the scheme’s construction costs to be withdrawn, citing concerns about the procurement process.
The motion, passed by 11 votes to three, reads:
“This Assembly notes with concern the many objections to the proposed Garden Bridge from a wide variety of individuals and organisations, from the Taxpayers’ Alliance to the Royal Society for the Protection of Birds. Objections have been raised over: the proximity to other crossings, the blocking of historic views of the Thames, the procurement process, the lack of cycling provision, the lack of a guaranteed right of way or step free access, the loss of over 30 mature trees on the South Bank, and the GLA underwriting ongoing maintenance costs running into millions.
“This Assembly believes that, with no cycling provision or guaranteed public right of way and given the proximity to other bridges, the project serves no transport function, and it is therefore inappropriate that £30 million of Transport for London money has been committed to it.
“This Assembly further believes that the public money earmarked for the project would be much better allocated to pedestrian/cycle river crossings where there is a genuine transport need, such as the proposed Brunel Bridge at Rotherhithe/Canary Wharf, or spent creating and improving green public spaces in other parts of the city.
“This Assembly therefore calls on the Mayor to agree to a full, independent audit of the procurement process, and to withdraw TfL funds from the project.”
