“Endless political wrangling” is responsible for the likely abandonment of London’s Garden Bridge project, its designer Thomas Heatherwick has claimed.

Last week London mayor Sadiq Khan said his office will not guarantee to underwrite the bridge’s operational and maintenance costs, if private funding and commercial operations can not cover them. Planning permissions for the bridge require such a commitment from the mayor.

In a letter to Lord Mervyn Davies, chair of the Garden Bridge Trust, Khan said the lack of all the necessary land use agreements for the bridge and a significant funding shortfall means the project is too much of a risk to the taxpayer.

Today (2 May), Heatherwick has given his view in an opinion piece written for the London Evening Standard newspaper – which has long supported the scheme, as has its new editor, former British chancellor George Osborne.

He said ending the project now, when “large sums of public and philanthropic money have been pledged and spent” would represent “such a missed opportunity and waste of resources.”

“Whatever the politics, to me as a Londoner this is saddening,” he said, adding that “it is always easier to stop an unusual new idea than to make it happen.”

Critics of the project – which would see a 366m-long footbridge supporting an expansive garden stretch from the top of Temple underground station on the Northbank to the South Bank – have hit out at the rising costs of the bridge, the restrictions that would be placed on members of the public wishing to use it, and the controversial procurement process that saw Heatherwick Studio win the contract.

In response, Heatherwick has claimed it would be a landmark for London. “What parent wouldn’t want to be able to stand with their child, in the middle of the greenest bridge in the world and marvel at the greatest city on Earth?” he wrote.

“I firmly believe it will happen one day. I just hope we don’t have to wait too long.”

The Garden Bridge Trust, which told CLAD it remains “very confident we can raise the remaining funds required” for the project, has not confirmed how it plans to proceed following Khan’s decision. It could request an amendment to the planning conditions from the local authorities involved.

In his own words

Thomas Heatherwick defends the plan for a garden bridge across the Thames

“I first got excited about the idea of a garden bridge when it was pointed out to me that despite having the best views in the whole city, the human experience of our river crossings tends to be of pavements attached to the side of dual carriageways.

“Anyone trying to look at the view is buffeted by wind and the cars, buses, lorries and motorbikes roaring behind you. And when you ask people if they have ever been asked to meet someone on one of London’s bridges, the answer is always “never”.

“The exciting question seemed to be whether a bridge could be an actual place rather than just a link.

“Creating calm, walkable and connected public spaces has become an urgently needed glue to hold city centres together.

“Anyone who has experienced the magic stitching of New York’s dislocated West Side by the raised High Line Park created on a disused railway line (whose creators have been advising the Garden Bridge Trust) can envisage what this can do.

“Our north bank hides an amazing wealth of medieval history, but new developments of luxury apartments risk cutting it off and creating a dead zone for pedestrians.

“The north and south banks feel like two different countries. Standing on Aldwych you feel a million miles from the relaxed energy of The Queen’s Walk.

“But a bridge of 366 metres, free to use, open every day, holding a garden created by amazing plantsman Dan Pearson, that you don’t get whooshed along by cars but lets you dawdle and gaze; that sounded to me like a completely new type of space that Londoners could get something from.

“I firmly believe it will happen one day. I just hope we don’t have to wait too long.”