The government repeatedly ignored advice not to risk pouring extra public money into the controversial garden bridge project, a damning new report has found.
The National Audit office found the government committed £30 million to the troubled central London footbridge, despite official warnings that they could end up with "nothing to show for it".
"The Department was at risk of losing up to £28.5 million with nothing to show for it as the Trust had not secured the land on the South Bank and it was not certain that the project would go ahead," they found.
Officials warned that the bridge, which had been personally championed by senior politicians including George Osborne and Boris Johnson, would bring little benefit, even if the Trust could secure the more than £100 million worth of additional private investment required.
"In the Department's view the Bridge was not predominantly a transport scheme, and as such did not align with any specific transport policies," they found.
"Wider benefits, such as those associated with tourism, were considered highly uncertain."
The Department for Transport increased its liability for the bridge three separate times, two of which were against official advice.
Last month London mayor Sadiq Khan, whose predecessor committees a further £30 million to the project, asked former chair of the public accounts committee Margaret Hodge to "investigate the conduct" of the last administration in authorising what would be the most expensive and controversial public footbridge in the world.
Politics.co.uk understands that the mayor and those around him are privately strongly opposed to the project, but are reluctant to publicly withdraw support at this stage.
However, Khan has committed to block any request for further investment in the project. Today's NAO report suggests there is a "pattern of behaviour" which suggests further requests may be forthcoming.
"If the project continues, it is possible that the government will be approached for extra funding should the Trust face a funding shortfall. The project has faced cost increases and delays to the schedule.
"The pattern of behaviour outlined in this report is one in which the Trust has repeatedly approached the government to release more of its funding for pre-construction activity when it encounters challenges. The Department, in turn, has agreed to the Trust's requests."
Opponents of the bridge today claimed the government had allowed personal relationships to blind them to problems with the bridge.
"This report is clear evidence that the Department of Transport had its arm twisted into supporting the Garden Bridge by George Osborne," Liberal Democrat London Assembly Member Caroline Pidgeon said.
"From the very outset personal interests overcame serious concerns about value of money for the taxpayer."
Transport Minister Lord Ahmad said:
"The Government remains supportive of the Garden Bridge project and ministers took into account a wide range of factors before deciding whether or not to make funding available.
“The taxpayer, however, must not be exposed to any further risks and it is now for the Trust to find private sector backers to invest in the delivery of this project. We will consider the NAO’s findings carefully.”
A Garden Bridge Trust spokesperson said:
"It is right that there is scrutiny of the project because it involves public money and transparency is good at an uncertain time. Seventy eight per cent of the Garden Bridge cost will be raised privately. The Trust has received an investment from Government of £60m which was always intended to kick start private investment. Of this £60m investment, £20m is being treated as a loan and around the same amount will be repaid to The Treasury in VAT. This means the public investment will sit at around £20m in line with the Millennium Bridge. This is a visionary project and represents a tremendous investment for the public.”