It said much about Boris Johnson’s eight-year performance as mayor of London that when the reviews came in, the highlight was often a fleet of buses. Designed by Thomas Heatherwick to satisfy some nostalgic, icon-hungry mayoral whim, they were widely taken at their instigator’s word to be an awe-inspiring success story, as well as one in the eye for “doubters”.

“They said I was mad,” Johnson crowed in 2013, in one of the Telegraph columns in which he would occasionally conduct an auto work appraisal, finding himself quite brilliant. Stop talking the buses down! He had seen Heatherwick’s bus, “a masterpiece of design”, being made. “I felt a sense of awe, and the deep certainty that this was the most wonderful project I had ever been involved in.” And given what he has done to his country since, that could indeed be the best epitaph he can expect.

Three years and the latest heatwave on, consumer experience confirms that the New Routemasters are definitely among the most amazing and extraordinary buses ever designed. Their windows, unlike those on standard buses, do not open. Their air conditioning is a disaster. Last week, the number of piteous, furious tweets from trapped commuters suggested that, three months since he stepped down, assessments of Johnson’s mayoral achievements may, like his buses, require urgent retro-fitting. “Hades” was a typical description. “Sauna”. “A special circle of hell. Send help”.

Passenger torment has intensified since the Routemasters, which came equipped with rear doors, an exemplary exercise in risk-taking, according to Johnson, stopped using conductors and ended up much like any other bus, albeit with no ventilation and in terms of galloping obsolescence up there with the iPhone. None, contrary to Johnson’s doubter-defying sales patter, has been exported. The new mayor, Sadiq Khan, has ruled out further orders.

If Johnson’s roving saunas are as unlikely to fascinate non-Londoners as they are Mr Johnson, given he is a cyclist with no reputation now worth losing, the huge gap between the sweaty hell of these vehicles and their comical overselling, should maybe focus minds on another mayoral first, his “garden bridge”. Unlike the London buses, this new masterpiece of Johnson-Heatherwick design is already, thanks to George Osborne, due to dun all taxpayers, not just Londoners, out of at least £30m of its estimated £175m cost. It will, however, still be closed for private parties.

Facebook Twitter Pinterest Taken for a ride? Boris Johnson on the platform of Thomas Heatherwick’s new London Routemaster in 2011. Photograph: Jonathan Hordle/REX Shutterstock

As tempting as it is to see the coming, river-hogging calamity as an ultimate demonstration in manspreading by its leading frontbench proponent, Johnson’s last fuck you to the city he has already defaced with hundreds of towers (overturning earlier assurances about the “precious skyline”), it is only fair to emphasise that its true begetter is Joanna Lumley.

As detailed in the Architects’ Journal, it was Ab Fab’s Patsy, with her grand projet hat on, who urged the newly re-elected mayor, in 2012, to look at a plan dear to her and fellow bridge fan Thomas Heatherwick. The structure was no less ridiculous, back then, for having cycle lanes (since abandoned), since it was already in the wrong place. A bridge was and is needed east of Tower Bridge, not close to existing crossings, in a central tourist trap.

But maybe it’s not so amazing that this particular whim was not immediately interred in the file dedicated to lovable A-list nuisances, or put out to tender to Lumley’s fellow actors, so as to compare it with, say, Helen Mirren’s Johnson-shaped colossus, Judi Dench’s entwined lovers sculpture, “Amitie Amoureuse”, or Felicity Kendal’s scheme for a massive triumphal arch, on the historic spot where he first saw the merits of Brexit. Lumley explained later: “I’ve known Boris since he was four, so he was largely quite amenable.”

The Architects Journal (alongside fine work from Rowan Moore, our architectural critic) has detailed the deeply suspect-looking process whereby the Lumley project, despite being spurious, aesthetically, environmentally and socially offensive, closed overnight, and a drain, in the belt-tightening era, on public funds, was finally handed to the original Lumley partner, Thomas Heatherwick. As for Johnson, the Lorenzo de Medici of the omnibus and cable car world, he declared it a “fantastic new landmark”. His colleague, the recently sacked art lover Ed Vaizey, called it “a fantastic vision”. Osborne, chucking in £30m, called it “iconic”.

Now, though, London is, at last, free of Johnson and the treasury of Osborne, yet their fantastic and iconic wheezes survive. Mysteriously, unlike the Cameron-era personnel and political strategies jettisoned overnight by Theresa May, Johnson’s bridge and Osborne’s infinitely more wasteful folly HS2 seem to have acquired, perhaps through familiarity, almost respectable status, for all the world as if they were not absurd vanity projects, backed principally by industry and hobbyists.

Sadiq Khan has pledged only to pause the supply of public funds, pending further investigation into the bridge, whose business plan, prepared along time-honoured Brexit lines, factors in a fortune in voluntary donations, from grateful pedestrians. Assuming pavements have not been missing a trick all these years, the shortfall will presumably be filled by taxpayers, bridge using and not. “The primary objective,” one analyst, Dan Anderson, commented last week, “is to get it built and the future will sort itself out.”

Facebook Twitter Pinterest HS2: George Osborne asked whether it would be visible from outer space. Photograph: HS2/PA

A not dissimilar philosophy appears to sustain the champions of HS2, as they ignore relentless, well-informed criticism from, among others, the National Audit Office, the public accounts committee, the Institute for Economic Affairs and, in May, a group of academic transport specialists. Adam Mills, the former chairman of Eurostar, called the economics “away with the fairies”.

Given the continued overcrowding on northern commuter networks due to be unalleviated by HS2, their passengers also appreciate, more painfully than most, how much less their difficulties signified in the chancellor’s infrastructure-addled mind than how quickly a businessperson could retreat from Leeds to the safety of the garden bridge. In his chastening long read , Simon Jenkins quoted an observer: for Osborne, the question was: “Could it be visible from outer space?”

A supporter of the bridge has argued that people only dislike it because it was championed by Johnson. That’s not actually true, but even if the bridge did not come to us from the Chelsea Flower Show school of naff horticultural fantasy, wouldn’t the foreign secretary’s endorsement, by itself, be reason to panic? From Michael Gove and New Routemasters, to Brexit and the debt we owe to (“Bravo!”) Assad, he’s been wrong about everything else. There’s an Ozymandias argument to made for immortalising Johnson’s serial misjudgments, but on this scale?

Similarly, it looks eccentric for Theresa May to humble George Osborne, ditch his policies, dump his tax and spending plans, then not divest her government, before it burns through the estimated £56bn, of the railway he planned for his legacy. Even if it is now this country’s fate to delight the rest of the world with one idiocy after another, it’s not too late to scrap Johnson’s bridge and Osborne’s train and pretend they never happened.