Travel around the periphery of any British town or city, and you will quickly behold a symbol of one of the most painful modern divides. The average residential care home will be set well back from the road, seemingly silent and apparently cut off from most of the life of the surrounding community. When people who know nothing of those inside glimpse such sights, what passes through their minds? Empathy, perhaps, with a family member living in such a facility; mounting awareness, maybe, of the rising care crisis and our collective failure to solve it. But what such sights could also embody is the widening divide between generations, and people leading completely separate lives.

Generation gaps are hardly new, but right now age arguably separates us as never before. The difference between the generations on Brexit is so familiar as to be a cliche, and the same division seems locked into politics generally. Only a decade ago, the 18-24s narrowly favoured Labour over the Tories by 31% to 30%, while 44% of the 65-plus demographic backed the Conservatives, with 31% voting Labour. The Johnson-Corbyn contest, by contrast, polarised the generations as never before. In the youngest age category, 62% of those who voted backed Labour, with only 19% voting Tory. Among 25-34s Labour also had a majority. But in the oldest part of the age range, the polarities were almost exactly reversed: 64% voted Tory and 17% supported Labour. Self-evidently, a party system defined by age is a terrifying notion, institutionalising mutual mistrust and resentment. But if we are not careful, that is exactly where we are going to end up.

What do millions of us really know about the lives of people at different stages of life from ourselves?

What is often overlooked is the fact that generational divisions are rooted in some of the deepest structures of society, not least our polarised housing economy. When I grew up in newly built 1970s suburbia, the ages of our adult neighbours ranged from new parents in their 20s to sixtysomething retirees. By contrast, new developments now often fall between stereotypical starter homes and separate houses and flats marketed at the over-50s. In some urban areas, council housing built for a wide range of people has long since been pushed into the private rental market and taken over by young professionals, while older, more rooted communities have dwindled. There and elsewhere, simple unaffordability has concentrated home ownership at the upper end of the age range, while the only option available to younger people is renting.

According to research by the Economic and Social Research Council, between 2001 and 2011, the number of neighbourhoods in England and Wales with high levels of age segregation doubled to more than 2,000. About half the population in London, Birmingham, Manchester and other urban centres is now thought to be under 30, whereas old people dominate rural and coastal places. Between 1991 and 2014, the number of areas where the median age of the population was over 50 rose sevenfold. In the wake of the EU referendum, it has become fashionable to fixate on the political gap between towns and cities. What has been overlooked is the fact that this issue blurs into questions centred on age to the point that the two are impossible to disentangle.

Facebook Twitter Pinterest ‘The Johnson-Corbyn contest polarised the generations as never before.’ Young anti-Brexit protesters in 2016. Photograph: Isabel Infantes/PA

As well as simple geographical separation, what divides the attitudes and values of older and younger people is the historic economic shift from what remained of the comparative security and stability of the postwar settlement, to an economy characterised by quicksilver unpredictability and the sense of a shrinking world. Younger people tend to see the 21st century’s openness, diversity and connectivity as the natural order of things, but want deep inequalities and imbalances to be corrected. Many older people, meanwhile, are thrown by the sense of constant change, and want to try to hang on to whatever security they feel they have. I do not think these two perspectives are quite as irreconcilable as some people think, but they nonetheless sit right at the heart of a deep generation gap.

This is hardly a favourable context for conversations about age, many of which are now coloured by a litany of insults, from “gammon” to “generation snowflake”, and lead to political dead-ends. Beyond close relatives, what do millions of us really know about the needs, values and lives of people at different stages of life from ourselves? Look at your Facebook friends. How many of them are significantly older – or younger – than you?

Last week, an innovative social enterprise called United For All Ages released a report titled Together in the 2020s. As well as sketching out a picture of worsening age segregation and rising loneliness, it brings together an array of voices to make suggestions that pull off a rare trick: channelling idealistic impulses into ideas that seem eminently realistic. There is stuff about intergenerational housing, ensuring schools and colleges are paired with social projects focused on older people, and opening up universities to a much wider age range. Pointing the way ahead, a Liverpool-based initiative called Homeshare UK facilitates people living with older homeowners rent-free, in exchange for “companionship and roughly 10 hours per week of help with agreed tasks”. In some Dutch cities, students have been encouraged to live alongside pensioners, trading free accommodation for “teaching residents new skills – like how to email, use social media, Skype and even graffiti art”.

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United For All Ages’ co-founder, Stephen Burke, wants to ensure new housing developments include homes suited to people across the age range, and enthuses about intergenerational initiatives that are already well underway. In Clapham, south London, a Jewish faith-based nursery – which is open to all comers – called Apples and Honey now shares its premises with a care home, ensuring older people get to mix with children and families. The story began with parent-and-toddler groups being held once a week at the Nightingale House care home, before something more permanent was established, alongside a cafe and restaurant, and arts facilities.

Here, it seems, is both a way of ensuring older people do not live in sealed-off silence, and a concrete example of how to bridge the generation gap, created in the spirit of self-help that now defines the kind of trailblazing change happening well beyond government. “Most of what we talk about is being done from the grassroots, by people pushing it on their own,” says Burke, although one of his big ideas is for a new Whitehall “Department of Connection”, “to join up and support intergenerational action nationally and locally”.

Clearly, beyond organisations and initiatives, all of this stuff demands huge shifts in attitudes and behaviour. Given its origins in the most basic aspects of how we now live, a new politics predicated on age isn’t about to quickly recede. We need to start to collectively change as a matter of urgency. The generation gap is perhaps the key element in Britain’s passage towards life as a deeply dysfunctional national family, brimming with resentment and mutual incomprehension. Before things turn even more rancorous, therapy is required.

• John Harris is a Guardian columnist