Last week, M&S received planning permission to demolish Orchard House, its flagship 1930 branch on Oxford Street. Orchard House was finished in 1930 to “Néo-Grec” designs by Trehearne and Norman, a distinguished practice that also designed many of the buildings on today’s Regent Street. It echoes its magnificent neighbour Selfridges, continuing the lines of its basement and cornice, emulating its giant order and spandrel panels, and working with it to form a splendid architectural frame to Orchard Street.

Its replacement will feature a familiar graph-paper facade, an unvarying grid of some two hundred exactly the same windows. M&S’s design and access statement claims ominously that “a rational structure is celebrated” in the new building.

This is not the only recent demolition of important interwar architecture. Indeed, it is not the only recent demolition in the City of Westminster. The mid 2010s saw the demolition of Premier House, a remarkable interwar Deco building on Oxford Street with polished black granite facades and bronze detailing. A few years later, Westminster City Council permitted the demolition of the Celanese House on Hanover Square, an elegant limestone building of 1928 with the slightly Egyptian detailing fashionable after the discovery of the tomb of Tutankhamun.

Across England, the story is similar. Many fine interwar traditional buildings are unlisted. Quite quickly, the interwar architecture heritage of this country is being destroyed.

These decisions are of that mysterious kind that are universally lamented as soon as they are taken, but that somehow happen anyway. Nobody argues that these were not good buildings. Nobody argues that London is made a more interesting, characterful and flavoursome place by the demolition of its Art Deco, Néo-Grec and Egyptian Revival heritage. Nobody argues that it is more environmentally friendly to replace these buildings rather than to refurbish and sympathetically extend them, as House of Fraser recently did to their Oxford Street branch. And yet, year after year, these buildings continue to be torn down. The question is: why?

The most admired sensibility in contemporary architecture is a catholic one, equally at home in a wide range of styles

Part of the answer probably is lingering contempt for non-modernist twentieth-century architecture in design and heritage circles. The standard narrative around this is well known. All previous societies, the story goes, had architectural styles of their own. Then in the nineteenth century, newly modernised Europe faltered, lacking the courage and the confidence to embrace a style commensurate with its modernity. Instead, it dressed up its buildings in revivalist costumes for some hundred years, before the modernist pioneers finally broke up the fancy dress party and inaugurated an honestly modern way of building. Buildings like Orchard House feature as the last vestiges of the cowardly and dishonest styles of the nineteenth century, and consequently have no significant heritage value. Whatever its problems, this story enjoyed enormous influence for much of the twentieth century.

This view is alive and well today. But it is probably no longer the orthodoxy. Among really elite tastemakers, it is regarded as slightly vulgar: as in other domains, the most admired sensibility in contemporary architecture is a catholic one, equally at home in a wide range of styles.

Nor is such a view obviously held in the relevant institutions — in the case of Orchard House, Westminster City Council, the GLA and Historic England. Studying the justifications they have given for their decisions, the prevalent attitude toward these buildings is not modernist hostility but vague indifference: Orchard House “represents a well-considered and sensitive response to the adjacent Selfridges” but nonetheless “falls well below the threshold necessary for listing”.

The main problem that interwar architectural heritage faces is rather different. The overarching criterion for heritage protection is “significance”. This is variously interpreted, but two features tend to be stressed: influence and uniqueness. This is all very well for the canonical works of the Modern Movement, a tiny number of buildings with a gigantic influence on post-war architecture. But the vast majority of interwar buildings in England are not modernist: they are Bankers’ Georgian, Deco, Wrenaissance, Classical, Tudor, Néo-Grec, Romanesque, streamline moderne, Expressionist, Egyptian, Gothic, or something else again.

This is a great and fascinating family of traditions, adapting and developing the old forms of British and European architecture to meet the problems of modern cities. But in an obvious sense it was lacking in influence, in that it was fated to die without successors.

Ten years after Orchard House, buildings like it had ceased to be built. By the end of the 1950s, every non-modernist architectural tradition in Europe was dead or almost dead. And ninety years later there is still no monograph on British interwar architecture that is not simply a history of the Modern Movement, and no histories of such non-modernist titans as Giles Gilbert Scott, Vincent Harris, Charles Holden and Austen Harrison. So in the short term, non-modernist interwar architecture was insignificant.

It is perhaps true that most interwar architecture fails against standard interpretations of architectural significance

The other problem that the non-modernist tradition faces is its determined reticence. Against what they took to be the bombast of the Victorians and the aggression of the modernists, interwar architects tended to value restraint, tact, and sensitivity to context. Where the Edwardians were drawn to the confidence and vigour of the Baroque, architects of the twenties and thirties were attracted to the discretion and understatement of the Georgians. Not for nothing was the greatest theoretical work of the inter-war decades, Trystan Edwards’s Good and Bad Manners in Architecture, a remarkably interesting and eloquent book in which the author champions respect for the street and the urban context.

Against the criterion of uniqueness too, then, interwar buildings tend to struggle: their designers were more likely to be trying to fit in than to stand out, to be the quiet background to public spaces rather than to dominate them. Though they draw on many styles, they rarely push those styles to extremes in the way that Victorian and Edwardian architecture did. Though they explored the possibilities of steel and ferroconcrete construction, they rarely made a fuss about it.  They are almost never intentionally disruptive, and, excepting some commercial Deco work, they rarely seek to be “iconic”.

It is thus perhaps true that most interwar architecture fails against standard interpretations of architectural significance. But perhaps that is so much the worse for those interpretations. For surely, a century on, the non-modernist buildings of the 1920s and 30s look increasingly sympathetic and far more sustainable.

Now, again, many people believe in designing buildings that conspire together to create harmonious streets and squares. Once again, many believe that the modernists were wrong to draw a harsh dichotomy between tradition and modernity, and that there may be many styles in which modern functions may be discharged and modern structural technology deployed. Re-using existing buildings, particularly when they lie within an existing settlement, is also far less hungry of that most precious of modern gasses — carbon dioxide.

Far from being creatively bankrupt, the non-modernist architects of the interwar period now look to have championed a deeply serious — indeed, a deeply significant — approach to architecture, which produced the last generation of generally popular buildings that this country has known.

That is why we at Create Streets have just launched the Diverse Modernities Project, devoted to celebrating and protecting the full range of Britain’s modern architectural heritage. We shall be making the case that re-using not destroying buildings like Orchard House is more sustainable and more popular. These buildings represent an approach to architecture that ought to be honoured and from which we have much to learn.

The unexpectedly intense outcry to the decision to destroy Orchard House suggests we may have come to a turning point. The Times, The Daily Mail, The Telegraph, The Guardian and The Architects’ Journal united to denounce the decision, as did the C20 Society and SAVE Britain’s Heritage.

The destruction of Euston Station in London and Pennsylvania Station in New York galvanised the movement for conserving Victorian era heritage, now almost universally triumphant. Maybe the moment has come for a similar reassessment of the heritage of a later generation.