From Covent Garden to Piccadilly Circus, Soho to Battersea Power Station, many of London’s most treasured historic buildings and areas were once threatened with demolition. Several proposals over the last century would have irreversibly changed the face of the capital, including a 1950s conceptual scheme for a giant conservatory supporting tower blocks over Soho and proposals a decade later to ‘replan’ Whitehall by demolishing virtually all the Edwardian and Victorian buildings around Parliament Square. Using the latest digital technology, a new exhibition presents the London that might have been and considers how the latest developments in digital mapping can be used in the future.

It is a deep mystery, one we may never fully understand. How and why a society more sophisticated than many assume poured vast resources and astonishing effort and ingenuity into works of no apparent use. Some say it was a ritual of cyclical renewal, some a statement of status by the elders and wise men of this society. For the most part we can only wonder.

I refer to the three-decade, multimillion-pound struggle to build (or rather, not build) a visitor centre at Stonehenge, which has seen several proposals come and go, architects hired and released, public inquiries held, politicians vacillate, and consultants paid for fruitless work. Budgets have been promised and slashed, and locations proposed and discarded. It has preoccupied the site’s guardian, English Heritage, for its entire existence, ever since it was created in 1984. The organisation’s first chairman, Lord Montagu of Beaulieu, declared his intention to solve the problem of Stonehenge, but had no more success than archaeologists have had in deciding what the old stones were actually for.

It was embarrassing. What greater task could the keeper of England’s heritage have than to create a fitting setting for the country’s ultimate ancient monument? This grand dither also occurred in the period in which the National Lottery came into being, which should surely have had few more important tasks – rather than sponsor centres of bogus ecology, highly branded vacuity or the Millennium Dome – than to help fix Stonehenge. If the mysterious Neolithic wizards who built it had had the modern genius for forming committees and machineries of indecision, they would still be in the Preseli hills in Wales, chipping away at the bluestones of which the monument is partly made.