The river Thames has long inspired a kind of architectural madness, the looping grey serpent driving many to attempt to leap its great breadth in ever more elaborate ways. As a student, John Soane proposed a triumphal bridge, a classical palace on piers that would have spanned the river with a domed temple, flanked by an avenue of corinthian colonnades. It won him the Royal Academy gold medal in 1776, but the plans have remained in a drawer ever since.
In the 1960s, a radical group by the name of the Glass Age Development Committee dreamed up a multi-storey pleasure bridge for Vauxhall. This would have straddled the Thames with a vertical stack of roadways, shops, skating rinks and a hotel, all topped with a roof garden and open-air theatre, but it proved one megastructure too far.
Not to be deterred, the Royal Academy organised a competition for a “living bridge” in 1996, won by the French architect Antoine Grumbach with a lavish suspended garden, lined with hedges, trees and an exotic “topiary cafe”. It was to hang from two vast apartment towers that would have paid for the project – but these generated fierce opposition that revealed the scheme as nothing more than green garnish for a lucrative private development.
Now there is another garden bridge plan. Bursting out of the river in the form of two conjoined mushrooms, it would create a floating forest between Temple and the South Bank, held aloft on a shimmering copper canopy. It is scarcely less improbable than the heroic failures that have gone before – and yet it seems very likely to happen. It has garnered not only the support of London’s mayor-cum-novelty-infrastructure-tsar, Boris Johnson, who has pledged £30m from his transport budget, but also the backing of central government, in the form of a further £30m from the Treasury. A detailed planning application has now been submitted, with the aim of having it built by 2018.