Given the controversial nature of the edifice designed by Turner Prize-winning architect Anish Kapoor, the latest figures are effectively a ball bobbling along the goal-line as far as its political (or aesthetic) opponents are concerned. And Duvall boots them jubilantly into the roof of the net.

Describing the ArcelorMittal Orbit Tower - to give it the official name - as “a vanity project of towering proportions”, Duvall adds: "It looks like we can now add the Orbit to the growing list of failed Boris Johnson pet projects alongside the Thames cable car, estuary airport and fault-riddled Boris bus.

“The Olympics was meant to be a grand celebration of sport, not an excuse to build pointless monuments at vast taxpayer expense."

For this, undeniably, unique edifice - jointly realised with £16 million ($26 million/€19 million) of steel supplied by industrial magnate Lakshmi Mittal and a balance of £3.1 million ($5 million/€3.7 million) supplied by the Greater London Authority - the devil is in the detail.

When the Orbit was re-opened in April 2014 following a revamp after the London 2012 Olympics and Paralympics, there were predictions of an annual total of 350,000 visitors. The total by March this year was just 124,000 visits. Problem.

As you might expect, the defenders of this twisting, asymmetric spiral of iron at the London Legacy Development Corporation, the body responsible for the redevelopment of the Park, are giving the situation another spin, describing the figure of “almost 200,000 visitors” as “a tremendous achievement.”

Notice is also directed to the additional attraction of “the world’s longest and tallest tunnel slide”, 178 metres long and 76m high, that will be woven into the entrails of the tower by Spring of next year.

“The descent will take about 40 seconds; average speed will be six metres a second, around 15mph,” says the official guide. “There are transparent sections on the slide so you can marvel at the view.”

Peter Tudor, Director of Visitor Services at Queen Elizabeth Olympic Park, asks: “What more exciting way to descend the ArcelorMittal Orbit than on the world’s longest and tallest tunnel slide?”

It sounds like that bolt-on is not going to do any harm at all to the visitor figures for what has already been marketed as both “the UK’s largest piece of public art” and “the world’s biggest sculpture”.

But will the big drop lead to rising visits? Or will the bottom line continue to slide downwards?

There are strong echoes here of the scenario which obtained when the Millennium Experience, housed to much fanfare in the Millennium Dome from January 1 to December 31, 2000, was found to have fallen well short of its expected annual visitor total of 12 million.

The figure was closer to 6.5 million, 3.5 million less than the 1951 Festival of Britain attracted in the space of five months. When the New Millennium Experience Company was liquidated in 2002, the Dome had taken £204 million ($316 million/€279 million) of extra Lottery funding due to visitor shortfall.

Prime Minister Tony Blair’s prediction at the Dome's opening - "In the Dome we have a creation that, I believe, will truly be a beacon to the world” - was looking like a rain-swept squib.

The intervening years, however, and the re-invention of all under the vast, Richard Rogers-designed shell of the Dome under the moniker of the O2, have shown the possibility of bad turning to good. To the point, of course, that the facility - temporarily and neutrally named the North Greenwich Arena - served as the venue for gymnastics and basketball at the London 2012 Games and continues to work as a sporting and entertainment venue.

There are ill omens for the Orbit, of course. The Skylon, the cigar-like structure suspended on the South Bank to mark the Festival of Britain in 1951, was toppled the following year on the orders of Winston Churchill and is rumoured to have been turned into ashtrays.

But perhaps the Orbit is going to be a slow burner. Rather like that other controversial steel edifice that got erected in Paris before the turn of the 20th century.

Originally, Gustave Eiffel wanted to build his tower in Barcelona to mark the Universal Exposition of 1888. But the inhabitants of Barcelona’s city hall thought it would be a strange and incongruous monstrosity.

So Eiffel transferred his project to home ground - where, when it was constructed as a centrepiece for the 1889 World’s Fair in Paris - it was widely denounced as an eyesore.

One letter published in a French newspaper deplored the prospect of looking out over Paris and seeing "stretching out like a black blot, the odious shadow of the odious column, built up of riveted iron plates."

The signatories included writers Alexandre Dumas and Guy de Maupassant, although the latter was later spotted dining regularly at the odious column’s highly reputed restaurant. Asked why he was there, considering his objections to the tower, he replied that it was the one place in Paris where one could not see it.

Well, let’s review the current status of the “black blot”.

It is now officially the most-visited paid monument in the world and 6.98 million people ascended it in 2011, a year after it had received its 250 millionth visitor.

In the meantime, the Orbit is supplementing the already established attractions of its viewing towers, distorting mirrors and high teas by introducing abseiling.  As we know from his zipwire experience, controlled descents have never been Boris Johnson’s thing. But perhaps his successor as Mayor of London will consider making a personal contribution to this towering project with a little publicity stunt of their own...