London narrowly missed out on a rare clash of the titans last September as, more or less simultaneously with England’s Ashes victory parade, something even bigger, sturdier and more awe-inspiring than Freddie Flintoff was set to lumber through Trafalgar Square. It’s hard to overstate the shock of turning a street corner and finding yourself face to face with a 40ft-high, 42-ton mechanical elephant. But if the visionary French theatre company Royal de Luxe had had its way, that deer-in-the-headlights stare so commonplace among the Australian batsmen last summer, as Flintoff bore down on them, would have been duplicated on the faces of thousands living and working in, or just passing through, Westminster.

The July 7 Tube bombings put the kibosh on this delicious piece of synchronicity, but the elephant is at least returning this May, even if English cricket victories are proving more elusive. And the most glorious thing about the experience is that it will have no obvious point whatsoever, but will nevertheless cause the most enormous, joyous, widespread disruption. Despite celebrating no anniversary, tournament or election, the elephant will take over large parts of central London for three-and-a-bit days and effectively shut them down.

As Helen Marriage, one of the event’s producers, happily concedes: “The first reaction is, ‘Why? Why would we do this?’ Even my mother asks me that.” She adds, however: “In Britain, we think it’s perfectly natural to divert the traffic for FA Cup- winners, the Marathon or state visits.”

Compared to sport and politics, art has never really staked its claim to the streets — indeed, say “street entertainer” in this country and it brings to mind isolated buskers, jugglers and the occasional sad, silver-painted figure trying to stand still while children prod it in the crotch. Royal de Luxe occupies a whole different universe.

Formed in 1979 by Jean Luc Courcoult, the company descends on towns and cities like a benign invading army. In one of their shows, Le Géant tombé du ciel, a vast Gulliverian puppet turned everywhere it went into an outpost of Lilliput. There was another giant in Les Chasseurs de girafes — created in 1999, after a year in Africa — but even that was overshadowed by a brace of crane-operated racing giraffes. Courcoult dreams up these situations, but it takes the genius of the designer/engineer François Delarozière to bring them to life. The elephant that is coming to London, and bringing with it a few other big surprises, took three years to build and requires a team of 112 performers and technicians. Purely from a mechanical point of view, the creature is a marvel. It takes three people just to work the trunk, and you can see the various other operators perched or clinging all over it like nerdy ticks. Every step is accompanied by a stomp-simulating spurt of air and, from time to time, the elephant soaks onlookers with its trunk from an on-board 380-gallon reservoir. There is a lot more to it than just the machinery, though.

For a start, this is not just any 40ft motorised elephant — it is, according to Courcoult, a 40ft motorised time-travelling elephant, built on the orders of a late-19th- century sultan so that he can pursue a similarly time-travelling little girl who has been haunting his dreams. On its back, the creature has a howdah containing the sultan, his servants and his courtesans, who periodically deign to put on a show for the crowds. When the sultan visited Nantes and Amiens last summer, he was greeted in a manner appropriate to visiting royalty; in London, he will be officially welcomed by the mayor, Ken Livingstone.

Forcing his host city to embrace the fantastical as if it were matter-of-fact is all part of Courcoult’s strategy. He aims, he says, “to bring out the child in every adult”, and remarks that he has seen grown people cry when one of his giants leaves town. “I don’t believe they are crying because he is leaving, but because of the loss of their imagination. Over several days, they have dreamt ... and now it’s finished.” The scale of his fantasy is cinematic and, crouched over his umpteenth red wine, teasing his hair into its best mad-professor patterns, he admits: “Yes, I would love to make films, but who would give me the money to do the things I want to do?” He compares himself to Napoleon (“The chance to redress injustices in Trafalgar Square, with my elephant ... who knows, I just might”) and, even more megalomaniacally, to a Cecil B DeMille who uses entire town populations as his unpaid cast of extras. “It is important that what we do is free,” he says, “and in public places. Audiences in cinemas or theatres have already crossed a threshold. They know they are there for art, and that is where they expect to find it. I want to reach people as they are and surprise them.”

The logistics of taking an entire city by surprise are daunting, and for Marriage, three years was barely long enough. Apart from the problems of fundraising in an area of the arts where, she says, “if governing bodies give you £20,000, they think they’re being generous — and something on this scale doesn’t happen for that sort of money”, there was an endless round of lobbying to be done. By the time she took an assortment of representatives from the Metropolitan Police, Transport for London and various branches of Westminster council to see the show in Nantes last May, they were “pretty much on board”, she says. “They thought it would be possible. But after they saw the show, they were so excited, almost breathless, discussing what they could do to make it work. That’s how seeing the elephant affects people. Suddenly, instead of asking ‘Why would we do this?’, the question becomes, ‘Why wouldn’t we?’”

The Sultan’s Elephant is in London from Thursday until May 7. For more details, visit www.thesultanselephant.com