Around fifteen years ago the actress Joanna Lumley had a vision. She imagined a bridge across the Thames with trees sprouting from it into the sky.

All of us with creative minds and who think about the places around is have had fun thoughts about where we spend our lives.

But luckily for Joanna an old family friend she had known since he was four was now Mayor of London. Boris Johnson, never one to miss a good photo opportunity and moment of frivolity, grabbed her vision and vowed to bring it to life. And he knew the man to do it.

Thomas Heatherwick was the current darling of design after his triumph with the Olympic Cauldron. So despite lingering issues with projects like B of the Bang in Manchester which was removed due to falling javelin-like spikes, and the overpriced, overheating new Routemaster bus for London, he got to work at creating this Garden Bridge.

There were some problems along the way. Because of European rules there had to be competition to procure a project architect. Two other firms alongside Heatherwick were asked to submit designs: Marks Barfield and Wilkinson Eyre, both established designers of world famous infrastructure and bridges.

But neither of them won the competiton and it was Heatherwick, with his pre-designed project already loved by Lumley and the Mayor, who was the victor – though there is now an investigation into the whole process.

There was also a small issue with the costs. Originally a totally privately funded venture the predicted budget began to rise. So it was decided that it should receive £30m from Transport for London and a further £30m from the national purse, and later added to with an underwriting of the annual £3.5m maintenance bill from public funds.

But this is all perfectly fine because we are promised a new park for the city. A relaxing and peaceful space to dwell and reimagine nature and the city. It will be a bucolic landscape of trees and grasses in which we can get lost and find ourselves at one with wildlife in the heart of a metropolis.

It will be great for the environment and provide a valuable and much needed transport link promoting pedestrianism and an ecological way of living.

But will it?

That is, at least, if you believe the spin and marketing half-truths from the Garden Bridge Trust who are behind the project. The reality is very different.

Another way of reading it is thus: A private development using £60m of public money which will not offer a legal public right of way may be built in the heart of London, blocking free and historic views from the South Bank towards Somerset House and St. Paul’s Cathedral as well as the world famous panorama east from Waterloo Bridge.

It will have a capacity of 2,500 people, so that relaxed romantic wandering may be less peaceful than implied. There’s also a queuing platform for a further 2,500 which suggests it may not be great for commuting.

A few minute’s walk along the South Bank is Waterloo Bridge which functions perfectly and connects the two banks of the river, so any claim that it offers critical transport infrastructure – the reason for that £30m from Transport for London – is arrant nonsense.

What of the ecological and environmental claims? The RSPB put out an outspoken press release (now replaced with a much weaker one), in which they stated:

“Water capture and storage as part of a wider drainage initiative would have been a bonus. Better still, it could link existing wildlife spots north and south of the river, but that’s not currently part of the plans. Londoners will not be gaining a new, wildlife rich habitat and, consequently, the bridge will not gain RSPB backing. 

“As supporters of green infrastructure in London, the RSPB can suggest much easier and cheaper ways to make life more pleasant for Londoners and urban wildlife.

“£175 million could do a lot to boost the way we manage water and waste or generate energy in the capital in ways that would clean our environment and better support some of the 60% of species currently vanishing around us. Indeed, Londoners can collectively add to the capital’s habitats and support much more wildlife than this £175 million bridge ever could.”

Natalie Bennett, leader of the Green Party, has also written about the “terrible greenwash of the Garden Bridge. The £60m of public funding dedicated to this folly could be used to create green spaces all over the city. Instead they are planning to fell trees and ruin open spaces on both sides of the river to create a private park with no transport value at all.”

The financial and environmental expense

It is fundamentally a private development with the pretence of greening the city while being quite the opposite – a few trees and plants will never repay the amount of carbon wrapped up in such a huge amount of concrete poured into the Thames.

The Garden Bridge Trust suggest the project will inspire people to consider the environment, and will engage people with the wonder of nature. But wouldn’t it be infinitely better if these goals were reached in a project which wasn’t at the same time damaging the world it wishes us to consider?

The cost is also questionable on reaching these aims, especially at a time when Kew is having its budget hugely cut and park keepers in Lambeth, where the Bridge lands on the river’s south side, are being laid off. At £175m, the Garden Bridge comes in at £76,000 per square metre – and that without any grass to sit on like, you know, a park has.

The other aim of the project, they say, is to “improve walkability” and they suggest that the bridge may be responsible for preventing 0.37 to 0.7 deaths a year due to improving health.

But given the proximity to existing bridges this idea that it would attract ‘new’ pedestrians is laughable, and any tiny benefit to an improved walking environment must be balanced against increased congestion along the South Bank after an extra 3m tourists have descended onto an already busy footpath.

Private space built over public space

That very same riverside footpath has an existing grassed area and thirty mature trees, a genuinely public and free space. It will be sacrificed should the Garden Bridge get built,replaced by commercial units, a platform for a 2,500 person queuing system and, when the bridge is not in public mode, a corporate entertainment space.

Instead of removing existent grassed areas and mature trees I suggest the £60m of public money (and £115m of private investment, should the sponsors still want to invest in it without the bling to hang their name off) could be far better spent improving the existing public realm across the whole of the city, and in the process improving and greening the parts of the city which can have an immediate effect upon the communities within London.

The Garden Bridge Trust also repeatedly claim that the project will improve pollination in another desperate attempt to paint the project as having a strong ecological footing. Sure, some trees and plants will help here, but at £650,000 per tree it’s an extremely expensive pollination project. All over London there are pocket parks, usually set up and managed by the local community.

I wrote about one such street where I live, Van Gogh Walk, in an article on my website, but they are all over – a recent Londonist series highlights just a few of them. These immediately benefit the community, they create a social space for activity, give local pride, can transform derelict spaces and stitch together main. And they genuinely improve walkability and pollination.

London doesn’t need monuments to egos offering no benefit to the very people who are paying for it and are most affected by it. That such a project is cloaked in false claims of environmentalism, localism and improvement in transport infrastructure makes it not only misleading but nearing fraudulent.

The greening of London and stitching together of communities can only happen from the bottom up, through public involvement, community and sincere environmental intent. This top-down private monolith of a Garden Bridge which imposes itself into one of the most admired parts of the city would be a disaster.

Compete: A Folly For London is a free-to-enter competition for satirical designs for the Thames South Bank public space which would be sacrificed to the private Garden Bridge. Deadline for entries is 28th August. See also on Facebook or Tweet @follyforlondon .

Campaign: Four ways to stop the Garden Bridge.

Will Jennings is a visual artist who used to work in architecture. His work has concerns in the politics, aesthetics and understand of the landscapes we build around us. Web: willjennings.info.