The mayor of London, Sadiq Khan, has formally withdrawn his support for a Thomas Heatherwick-designed Garden Bridge across the River Thames; bringing a likely end to a project that has fiercely split opinion.

In a letter to Lord Mervyn Davies, chair of the Garden Bridge Trust, which has been overseeing the controversial crossing, Khan said the lack of all the necessary land use agreements and a significant funding shortfall mean the project represents too much of a risk to the taxpayer, particularly with planning permissions due to expire in December.

“The funding gap is now at over £70m and it appears unlikely that the trust will succeed in raising the private funds required for the project,” he wrote. “I am simply not prepared to risk a situation where the taxpayer has to step in and contribute significant additional amounts to ensure the project is completed.”

He acknowledged the Trust’s repeated argument that delays caused by third parties was restricting it from approaching private funders, but said “there will always be challenges and third party issues on a project of this nature.” In reply to the Trust’s assertion that donors have promised additional funding, he said that pledged funds are lower than two years ago, adding: “And of course, a pledge is not the same thing as a payment into your account.”

The mayor added that beginning construction before all private funds were in place would run the risk of leaving the city with “a partially built bridge which would either require completion or demolition” at the expense of the public.

The decision follows the publication of Dame Margaret Hodge’s review of the project, which found decisions on the Garden Bridge “were driven more by electoral cycles than value for taxpayers’ money” and “the original ambition to fund the Garden Bridge through private finance has been abandoned.”

The report also described the Trust’s finances “as in a precarious state” and said there “was not an open, fair and competitive process.”

Hodge found that original cost estimate of £60m was likely to rise to more than £200m, adding that £37.4m of public funds have already spent without any building work having started.

In response to Hodge's findings, Davies said: “This report, with its many errors and ill-informed opinions, is no basis upon which to take decisions about a project that has been through the complex democratic processes by which decisions on development are made in this city.”

In a statement released today (28 April), responding to Khan's letter, the Trust chair said: "We received the mayor's letter with great regret today. We will study the contents of the letter in detail before responding formally. The Garden Bridge Trust was set up at the request of Transport for London and the Department of Transport to deliver the project which had received public money.

"We have had enormous support from our funders and are very confident we can raise the remaining funds required. But sadly the mayor of London has taken a different decision to those in place when the project started.”

While Khan is not able to formally scrap the project, the planning permissions for the bridge are dependant on its future operational and maintenance costs being guaranteed from mayoral funds, if private funding and commercial operations can not cover them. The Trust could now request an amendment to these planning conditions from the local authorities involved.

Khan’s predecessor as mayor, Boris Johnson, and the former Chancellor of the Exchequer, George Osborne, were champion of the scheme – the brainchild of British actor Joanna Lumley.

In response to critics who questioned the need for the bridge, its cost and the restrictions that would be placed on members of the public wishing to use it, supporters argued it would become a new landmark for London, boosting regeneration and economic growth on both sides of the Thames.

In an interview with the BBC last year Heatherwick asked, “How can it possibly be a bad thing to stitch the city together better, to create new public space that we have never had before, to create new views for all of us?”

He added the project has been used as a political football by “people with an agenda” and those “who love to sneer.”

His design envisioned a 366m-long footbridge stretching from the top of Temple underground station on the Northbank to the South Bank. Pedestrian paths would wind through an expansive garden created by landscape designer Dan Pearson.

I will not be providing Mayoral guarantees for the Garden Bridge Project - my letter to the Chair of the Garden Bridge Trust. pic.twitter.com/xg6jzhZ0Zs

— Mayor of London (@MayorofLondon) April 28, 2017