Boris Johnson has rebuffed criticism of the Garden Bridge procurement process, claiming that the project's delivery model is "proving successful" and could be replicated.
Transport for London this week published an exchange of correspondence between Jane Duncan (president of the Royal Institute of British Architects), Mayor of London Boris Johnson and TfL commissioner Mike Brown.
Earlier this month Ms Duncan went public on her concerns about the process that led to the selection by TfL of Heatherwick Studio and Arup to work on plans for a footbridge across the Thames between Temple and South Bank.
Both Mr Johnson and Mr Brown take Ms Duncan to task for relying on media coverage of the Garden Bridge when commenting on the scheme.
"Recent allegations by members of the press that the procurement processes followed by Transport for London were not judged fairly and transparently are wholly unfounded," wrote the Mayor.
He added: "I appreciate that the model of delivery being adopted for the Garden Bridge is a novel one, and this may have confused some commentators in the media."
Mr Johnson goes on to claim that "the model for delivery of this project is proving successful and I am optimistic about its potential for replication in future to deliver other wonderful additions to London's landscape through private endeavour and charitable donations.
"The public funding element of the project is being used to secure considerable private sector investment – currently at £85 million ... and rising, which is a huge achievement."
TfL boss Mike Brown followed up the Mayor's letter with his own reply to the RIBA president, insisting that "the process which we followed was transparent and fair to all parties concerned" and blasting "false reports and statements" about the Garden Bridge.
Mr Brown was stronger in his criticism of Ms Duncan, noting his "disappointment that having written to the Mayor about your concerns you chose to provide comment to the press immediately, before giving the Mayor or TfL an opportunity to respond.
"With so much incorrect reporting it is not helpful in my view when respected members of the professional community elect to speak with the press before providing all parties the opportunity to clarify the facts of the situation."
Jane Duncan has subsequently written again to Mr Johnson and Mr Brown reiterating her call for an independent review of the Garden Bridge procurement process.
She told the Mayor: "I know you will share my concerns around the need to reassure the public that their money will be spent effectively by TfL and hope you will be able to use your remaining time in office to do that."