Well, it’s been fun. Watching the slow drip of negative information about the Garden Bridge has become something of a spectator sport for some Londoners. But with a construction start date rapidly approaching, it’s time to stop playing and put this thing back in its box.

Let’s start with the assumption that we need a pedestrian bridge between Temple and the South Bank. It’s not a crazy one: the gap between Waterloo and Blackfriars bridges is about the same as that between Blackfriars and Southwark before the Millennium bridge came along. But if the purpose of a bridge is to quickly move people between two points, this bridge fails. The Garden Bridge Trust estimates it will take 12 minutes to cross — an inordinately long time, and the same amount of time you’d take to get between the two points by taking a detour via Waterloo bridge.

I recently met the Chief Executive of the Garden Bridge Trust who, despite having enthusiasm in spades, couldn’t elaborate a transport need for the bridge beyond ‘Waterloo bridge isn’t nice to walk along’ (tell that to The Kinks) and ‘it’ll help open up the Strand’ (an area which is hardly undervisited).

It feels very much like attempting to retrofit a reason onto an idea someone (Joanna Lumley) once had. RIBA, in a document explaining the background to the bridge, says “there is no objective reasoned analysis, evidence or comparative study as to what problem is being solved or function fulfilled pre-dating the design solution”.

There are so many problems with the Garden Bridge — why no provision for cyclists? Why isn’t it open 24 hours a day? Why can it be closed if the Trust needs to hold a fundraising party? What will be the effect of all these people on the already crowded South Bank and the deliberately peaceful Temple Gardens? How on earth does it take 12 minutes to cross? — but the one that’s becoming increasingly serious is what looks like favouritism in the selection of design and designer, and a scandalous misuse of public funds.

The short version: Heatherwick Studio, which had been working with Joanna Lumley on the concept of a garden bridge for some years, won a tender to “help progress ideas for a new footbridge” over two much more experienced firms. Those firms outlined in detail how they would study the parameters and constraints to work out options. According to RIBA, Heatherwick Studio’s submission included, rather presumptuously, its design for the Garden Bridge. Late. With cost estimates far in excess of the other bids. Yet the company still came top of Transport for London’s scoring system — a system that nobody quite understands, because documentation has been destroyed.

Boris Johnson, while Mayor of London, met Joanna Lumley and Thomas Heatherwick before the bidding process started. He even went with Heatherwick and Isabel Dedring, then Deputy Mayor for Transport, to Apple in San Francisco in an attempt to secure funds for what was then intended to be an entirely privately funded project, again before the tender process began. The former Mayor has responded with bluster and insults to questions about the propriety of these meetings — which is generally what happens when he’s on the back foot.