Hospitals are mysterious, self-contained places, but also central to our lives. They occupy a ritual role as the locations for the most extreme moments of human existence – birth, crises and death – as significant as churches once were. Yet, as buildings, they can be almost invisible, secondary to the functions they perform.

In London more than 500 hospitals have closed, most during the past century. The lost hospitals of London, from the showy high-Victorian complexes to the obscure, specialist hospitals that once dotted the city, retain a shadowy presence in familiar neighbourhoods.

The London streetscape I hold in my mind is punctuated by abandoned and converted Victorian hospital sites, peculiar medical buildings reassigned to new uses, and gaps where a presence lingers.

The meat-free medics

A small, oddly shaped park beside the New Kent Road in south London has lodged itself in the back of my mind. Within sight of the seething Elephant and Castle gyratory, it is a kink in the street line, creating an awkwardly sized space occupied by low-maintenance landscaping.

It stayed with me for years as unexplained, just one of the many leftover spaces strewn around London, but perhaps also a problem to be solved.

The missing piece clicked into place when I read about the long-closed Hospital of St Francis, patron saint of animals, once located at this spot. A remarkably radical institution for its time, the hospital had been founded in 1898 by a Dr Josiah Oldfield, on vegetarian principles. Oldfield was at university with Mahatma Gandhi, where they jointly founded the Fruitarian Society, and the two shared a flat in Bayswater.

The hospital allowed no meat in the building, which led to early resignations from staff who had not read the small print. This minor revolution in an unremarkable location was typical of the gloriously varied world of hospitals operating in London right up until the foundation of the National Heath Service in 1948.