Boris Johnson’s mooted bridge to France joins a select club of the daftest schemes dreamt up by architects and engineers.

Mon dieu! Foreign secretary Boris Johnson has mooted building a 22-mile bridge to France. The ex-London Mayor is no stranger to éléphants blancs and this latest one joins a select club of the daftest schemes dreamt up by architects and engineers.

Johnson’s proposal was clearly floated as an attempt to foster a bit of entente cordiale during President Macron’s otherwise tetchy Anglo-French summit. He tweeted: “Our economic success depends on good infrastructure and good connections. Should the Channel Tunnel be just a first step?”

Errr, yes, would seem to be the obvious response, but Macron appeared to play along with the conceit, with the Guardian reporting that he supported the project. Downing Street, however, gently deflated expectations by briefing journalists that there were currently “no detailed plans” for the project.

Johnson is no stranger to promoting fabulously expensive but gimcrack projects that were in reality never going to be build.

Most spectacular, of course, was the ‘Boris Island’ Airport, a £90bn, four runway artificial island in the Thames masterminded by Lord Foster. I recall writing a column for Building in 2011, ahead of the final decision on South Airports, suggesting “it won’t fly”. And it didn’t.

Boris has already unsuccessfully backed a bridge, the Garden Bridge. Despite the patronage of Joanna Lumley and assorted luvvies, the pedestrian Thames crossing was spike last year and £46m of public money floated down the Creek.

With his crazed mop of white hair, Boris looks for all the world like the film world’s greatest exponent of doomed grands projets, Fitzcarraldo. The imaginary 19th century rubber baron, played in the film of the same name by Claus Kinski, was thwarted in his bid to build an opera house in the depths of the Amazon. The hapless venture, immortalised in the Werner Herzog art house movie, involved dragging a ship over a mountain.

You can’t keep a good megalomaniac down. Given he kept badgering government for years to choose Boris Island over the far more practical choice of Heathrow expansion, he’s not going to drop a second Channel Crossing, or ‘CX2’, in a hurry. But it won’t be built.

An even more bonkers transport pipe dream was the 60-mile tunnel across the Irish Sea proposed excitedly in 2004 by the Institute of Engineers of Ireland. It would link Fishguard and Rosslare and would link with a high-speed rail line connecting Belfast, Dublin and Cork.

Nothing excites the Futurist more than a bit of magnetic levitation. UK Ultraspeed, a ‘maglev’ train line between London and Glasgow, linking 16 stations including Edinburgh, Birmingham, Manchester and Newcastle and six airports. It was finally dropped in 2007.

But the ne plus ultra of doomed fantasies was architectural collective Archigram’s “Walking City” of multi-storey buildings mounted on giant, telescopic steel legs, published in increasingly lavish detail during the early 1960s, but with scant attention to practicalities.

Maybe Boris could revive the notion. Rather than fighting about where the financial capital of Europe will be located post-Brexit, we could pack thousands of investment bankers into one of the pods and march them back and forwards across La Manche.