The plug should be pulled on the contentious Thomas Heatherwick-designed Garden Bridge, despite over £45 million of public money already bound up in the project, according to a new report.

Update 28/04/17: London mayor Sadiq Khan has now withdrawn his support for the Garden Bridge.

Labour politician and former chair of parliament's public accounts committee Margaret Hodge was asked to carry out the review by London mayor Sadiq Khan to assess whether the project to build a plant-covered bridge across the River Thames is a good use of taxpayers' money.

Hodge's report has found that the scheme, which started out with an estimated price tag of £60 million, is now likely to cost over £200 million. As a result, it determined that the taxpayer would be better off if the bridge were cancelled.

"I did not seek to ask whether the concept of a garden bridge over the River Thames is a good idea. But my review has found that too many things went wrong in the development and implementation of the Garden Bridge Project," said Hodge of the report.

"Value for money for the taxpayer has not been secured. It would be better for the taxpayer to accept the financial loss of cancelling the project than to risk the potential uncertain additional costs to the public purse if the project proceeds," she continued.

"In the present climate, with continuing pressures on public spending, it is difficult to justify further public investment in the Garden Bridge. I would urge the Mayor not to sign any guarantees until it is confirmed that the private capital and revenue monies have been secured by the Garden Bridge Trust."

So far £37.4 million of public money has already been spent on the 367-metre-long bridge, with additional funding underwritten by the British government bringing the cost to the taxpayer up to £46.4 million if the project were cancelled.

The Garden Bridge Trust responsible for carrying out the project has lost two major donors since the outset of the project, only managing to secure £69 million from private funding.

This leaves a gap of at least £70 million needing to be raised for the capital investment. There have been no new private pledges since August 2016.

"Decisions on the Garden Bridge were driven by electoral cycles rather than value for money," the report reads.

"From its inception when there was confusion as to its purpose, through a weak business case that was constructed after contracts had been let and money had been spent, little regard has been had to value for money," it continues.

Commenting on the report, Garden Bridge Trust chairman Mervyn Davies said: "We are pleased that Dame Margaret has finally published her report after six months of uncertainty."

"We will be studying the report in detail and seeking a meeting with the Mayor to discuss next steps," he continued. "The Trust remains as determined as ever to make the Garden Bridge happen which will bring huge benefits to London and the UK."

The report also raises concerns about the contracting of Heatherwick Studio and Arup, stating "procurement options were intentionally developed to enable Heatherwick Studio to qualify".

"The procurements subject to this review comprised one contract that was awarded to Heatherwick Studio for design and consulting services and one contract that was awarded to Arup for engineering and project management services," it reads.

"These were not open, fair or competitive procurements and my review revealed systemic failures and ineffective control systems at many levels."

British designer Thomas Heatherwick first unveiled designs for the Garden Bridge in 2013.

The tree- and plant-covered bridge was designed to span the River Thames between Temple and the South Bank and feature "super-strength" copper-nickel skin covering its underside and legs.