In a gushing article on the designer Thomas Heatherwick, published soon after it was announced that Sky TV would sponsor his proposed garden bridge, Richard Morrison of the Times wondered why the project attracts opponents “whose hostility seems implacable”. Why indeed? Why should so much anger be stirred by a project that started with Joanna Lumley’s innocent and benign dream of commemorating Princess Diana by projecting greenery across the Thames? Why should so many want to trample on Joanna’s flowers?

Well, I can’t speak for the Ramblers’ Association, the Dean and Chapter of St Paul’s Cathedral, the Royal Society for the Protection of Birds, the guerrilla gardeners and structural engineers who have seen it as a travesty of their crafts, the residents of the areas near its landings, the lawyers of the Middle Temple, the president of the Royal Institute of British Architects, the Taxpayers’ Alliance, the Metropolitan Public Gardens Association, the Green party, the Liberal Democrats, and the various others who have raised doubts about the project. Nor will I dwell here on the well-aired reasons to be doubtful: the blocking of well-loved views, the spurious claims for usefulness and sustainability, the clumsiness of the design, the cost to the public, the potential impacts of crowds, the likely effects of private sponsorship on allegedly public space, the many ways of both crossing the Thames and greening London that would cost less.

But, speaking for myself, what really provokes are the half-truths, deceptions and evasions with which the project is promoted and sold. Take the deft manoeuvre whereby brief rebellions by the Labour mayoral candidate Sadiq Khan and the leader of Lambeth council Lib Peck were neutralised. Khan and Peck had expressed concern about its cost to the public purse: £60m plus an uncertain liability for the estimated £3.5m per year running costs. They and Transport for London, which had been due to put up half the £60m, and the Garden Bridge Trust then went into a huddle, from which it emerged that TfL’s contribution would be limited “to £10m rather than the original £30m contribution.”

Peck felt enabled to declare victory and withdraw her opposition: “I’m pleased that Londoners are getting a better financial deal,” she said, “particularly at a time of austerity when all public sector organisations are being forced to make deep cuts to services. We’ve been in tough negotiations … and we’ve successfully agreed a deal that will cut London taxpayers’ contribution towards the garden bridge by two thirds.”

This left the national taxpayer – no less than Londoners in the grip of austerity and tough choices on spending – with an undiminished obligation for the £30m promised by the Treasury. It also turned out that TfL’s payment had not so much been reduced as converted into a loan, to be paid back at a distant point in the future, if at all, which is in the end not much of a concession.

Or else there is the story of the processes by which Heatherwick and his team were appointed to design the bridge, whose layers of murk have been penetrated by persistent reporting by Will Hurst of the Architects’ Journal, and which last week caused both the London Assembly and the president of the Riba to say that the project should be halted pending proper scrutiny, and has prompted Khan’s off-on support to wobble again.

Heatherwick had long been working with Lumley in the days when it was intended to be a free gift from private sponsors to the citizens of London. It was then decided that public funding would be needed, at which point it became subject to the rules whereby major public projects are commissioned. There has to be an element of competition, to establish that taxpayers are getting the best people for the job, at the best price. Two additional design teams were invited to tender.

Heatherwick won. There is nothing wrong with that, except that the decision was based in part on an assessment that he was better qualified for the job than the other two practices, both of whom had considerably more experience of designing bridges. This judgment appeared to have made by one man, TfL’s Richard de Cani in a way that, as he was forced to agree when questioned by the London Assembly, was inconsistent with TfL’s procedures. De Cani is now going to work for the engineers Arup, who are working with Heatherwick on the bridge, as he is entitled to do, but his departure underlines the need for assessments to be made by a broad-based panel who cannot be accused of favouritism.

It also emerged that, before the selection process was carried out, Boris Johnson flew to San Francisco so that he and Heatherwick could ask Apple to contribute a sliver of their billions to help pay for the Heatherwick-designed bridge. This suggests that Heatherwick was already seen as the project’s likely designer.

View from the bridge: ‘preordained reality, in the face of which facts, rules and opinions must be bent’ . Photograph: Courtesy of Heatherwick Studio

Or you could take the Garden Bridge Trust’s impressive-looking claim that nearly 80% of Londoners support it. This is based on a ComRes poll that asked respondents if “they supported the proposal for a garden bridge”. It didn’t spell out the costs, risks or doubts, or ask if people thought that it was the best use of public money, or consult people outside London who would also have to pay for it. In which circumstances the result is hardly surprising. It is like asking people if they would like a free holiday. As someone who has nothing against gardens on bridges, if they do what they are supposed to do without unacceptable impacts, I might have said yes myself.

The common theme is an attitude that the bridge is a preordained reality, in the face of which facts, rules and opinion must be bent. It assumes that power of networking and spin will prevail. It has been sustained among other things by the relentless cheerleading and propagandising of London’s Evening Standard, to which, with Sky’s sponsorship in place, might now be added something similar from the Murdoch media. When debate on a significant project is deflected and numbed, it is frustrating for those who want to raise reasoned objections, which would be why the opposition is so implacable. More than that, it is no way to make major decisions in a democracy.

• This article was amended on 15 February 2016. An earlier version said that Heatherwick had travelled to San Francisco with Boris Johnson for a meeting with Apple.

