The news that Boris Johnson has rubber-stamped the garden bridge should come as no surprise. Since taking office he has become the self-styled tsar of novelty infrastructure projects, bestowing London with an empty cable-car (the Emirates Airline doesn’t see a single regular user according to recent TfL figures) , a fleet of sweltering buses and misty renderings of a glowing airport floating in the estuary. But what is staggering is quite how quickly a plan for a private tourist attraction planted in the centre of the city, at the whim of a celebrity, has been swept through the planning system – and taken £60m of public funding with it.

Joanna Lumley has been peddling her idea for “a chance to walk through woodlands over one of the greatest rivers in the world” for more than a decade, but Boris has been the first to take it seriously. She originally conceived the project as a Princess Diana memorial bridge and pitched it to Ken Livingstone in 2002. He had the good sense to turn it down, but she has now managed to seduce City Hall, Lambeth and Westminster councils alike with a liberal sprinkling of architectural fairy-dust, courtesy of “the Da Vinci of our day” Thomas Heatherwick – who also designed the Boris Bus.

It has since emerged that the miraculous garden bridge is neither a garden nor a bridge. It will provide a planted area less than half the size of a football pitch, will be closed to the public at night and will require advanced registration for groups, in order to discourage protesters. Nor will cyclists be allowed in. It is projected to attract crowds second only to Disneyland in Europe, at one of the busiest stretches of the South Bank, leading local critics to describe it as “another Hillsborough disaster in the making”.

It has been vociferously opposed by residents on both sides of the river, by St Paul’s cathedral and by the barristers of Middle Temple – who have declared Lambeth’s planning decision unlawful. The Westminster committee reached the height of farce when the entire decision came down to a judgement over whether the joy brought by new views from the bridge would outweigh the damaged caused to existing cherished views; imaginary views that weren’t even provided in the planning application.

The decision sends the signal that, like the rest of London, the Thames is now a playground for the construction of private fantasies – that will be furnished with public funds to achieve them.