There is a scene in Denys Arcand’s 2003 film The Barbarian Invasions, in which a young French antiques appraiser visits a Quebec Catholic church to size up some long unused religious artefacts the local priest is trying to offload. The priest shows her around a dusty lock-up and tells her: “Quebec used to be as Catholic as Spain or Ireland. Everyone believed. At a precise moment, during the year 1966 in fact, the churches suddenly emptied in a matter of months. A strange phenomenon that no one has ever been able to explain.” The irony of course is that churches would in time also empty, or at least become emptier, in Ireland and Spain. This scene however sums up eloquently the material legacy a societal decline in religious faith leaves. Stripped of their function in a thriving congregation, surplus ciboria, chalices and tabernacles of modest craftsmanship become items of largely worthless bric-a-brac. (It is interesting though that all three of those items endure as living, breathing examples of Quebec French’s wonderfully colourful profanity.)

In many Western countries (but clearly not all), the decline in church-going has seen the patrimony of churches threatened, particularly ones in smaller towns and villages that cannot harness their appeal as tourist attractions. About 30 Church of England churches are closed for worship every year and more than 1,000, of all faiths, have been made “redundant”, as church jargon calls it, since the 1960s. The decision is pragmatic, with the cost of maintaining the buildings to cater for dwindling congregations becoming prohibitive. The churches, once deconsecrated, find new lives as residential properties, village halls, bookshops, libraries, theatres, concert venues or gastropubs. They also sometimes become places of worship for other faiths – these days most often mosques or Evangelical churches. Not that that is an entirely recent development either – the Brick Lane Mosque started off as a Huguenot chapel in the mid-eighteenth century, and then became a Methodist church and a synagogue before taking on its current incarnation in 1976.

France, a country which has seen a similar decline in church attendance, has a different approach. The 1905 law ordaining the separation of Church and State ruled that all churches built prior to that date would become the property of the state, which would henceforth be responsible for their upkeep. It is an unusual responsibility to take on, especially in the light of the law’s avowed intention, but it works reasonably well, allowing the churches to benefit from the expertise and resources of state conservation agencies. The state is also now prohibited from funding the construction of new churches (except in Alsace and Lorraine, exempt because they were German in 1905) so organised religion is responsible for taking care of anything built since the law was enacted. Not that all churches have been saved from oblivion but only 400 out of some 44,000 are believed to be in material danger, which is not bad in a country where only 4.5 per cent of the population are regular church-goers.

France, which was already the epicentre of the flowering of great Gothic architecture of the Middle Ages, has also continued to build some great churches, with a stab at ecclesiastical architecture being de rigueur for many of the great French or French-based architects, such as Victor Baltard, Gustave Eiffel, Le Corbusier, Auguste Perret and Claude Parent; there were also renowned church-building specialists such as Pierre Paquet and Jacques Droz. Despite its testy relationship with organised religion, France loves its churches and they are indelibly embedded in both the landscape and the country’s cultural history. Churches also rarely end up being used for other purposes. Though the Jacobins and Communards both commandeered churches for profane uses (as did other iconoclasts such as Oliver Cromwell and Enver Hoxha), the Priory of Saint-Martin-des-Champs (now the Musée des arts et métiers) and Jacques-Germain Soufflot’s Panthéon are among the few prominent churches that became permanently secular. Many of the aforementioned jewels of Gothic architecture, such as Notre Dame de Paris, Sainte-Chapelle, the Basilica of Saint-Denis and the cathedrals of Rouen, Chartres and Reims each draw hundreds of thousands of tourists each year (and manage to avoid admission fees such as St Paul’s Cathedral’s gobsmacking £18.50). But humble parish churches are also affectionate landmarks for even non-believers and non-Christians. When I first arrived in Paris, I was amazed to find a church in Beaubourg that showed art-house films on Sunday nights, and Jacques Delors, later European Commission president, in the 1950s ran a film club in the church I can see from my window in the eastern neighbourhood of Ménilmontant.

Even as they might administer to fewer parishioners these days, many churches in Europe still retain vital functions – they have become centres of both worship and socialising for immigrant communities, such as St Peter the Apostle church in Woolwich, and the Igreja de São Domingos in Lisbon, both of which attract African immigrants. Churches across Europe have also been literally refuges for migrants and refugees. And even among the more spiritually feckless, churches remain a favoured choice as wedding venues, though the superficial interest and opportunism often strains the patience of pastors.

Some churches are incongruous in their present locations, such as the 800-year-old Oude Kerk in the midst of Amsterdam’s red-light district, though there is a certain Bunyanesque aptness about a Calvinist church’s close proximity to sin. The “meaning” of a church has changed for many of us who don’t believe, but that doesn’t mean churches cannot be welcoming places – there is nothing I love more than to go into an unknown church and sit for a few minutes in the calm. There is an architectonic ambience imparted by churches, even the less spectacular ones, that few other buildings give off. There are churches in some unlikely places that I hold close to my heart, such as Sigurd Lewerentz’s red-brick Markuskyrkan, suffused with Nordic warmth, in a Stockholm suburb or Jože Plečnik’s concrete Church of the Holy Spirit in Vienna. As well as being architecturally fascinating, they feel faultlessly right. For this reason I am not a big fan of churches being converted for more practical uses when abandoned by the religious. The resultant effect is invariably kitsch or one of petit-bourgeois propriety. It is, of course, sacrilegious (from a conservationist point of view) to say this but I would sooner let them turn into elegant ruins or, as the French, those great connoisseurs of church architecture, have done so many times throughout history, knock them down and build something new in their stead.