A month after Labour’s dizzying defeat, there is unsurprisingly not much agreement, yet, about what the party should do next. But there is one thing on which the leadership candidates, many party activists, and political journalists and commentators of all persuasions seem to agree: Labour needs to reconnect with its heartlands.

As a political term, “heartlands” is vague but potent. Heartlands can be electoral, emotional, historical, geographical, or a combination of all these. Yet in the current conversation about Labour, the word is fast acquiring a particular meaning. That meaning is politically loaded. It could also lead the party up a dead end.

In speeches and newspaper articles these days, Labour’s heartlands are almost always characterised as “traditional” or “working class”, “industrial” or “ex-industrial”, “northern” or “in the Midlands”. When specific places are cited, they are often former mining villages, or left-behind towns – places where Labour voters can be quite socially conservative, culturally and racially homogeneous, and suspicious of dramatic shifts in the party’s direction. The implication is that these are the voters the party should rebuild itself around.

Meanwhile, all this talk rarely mentions urban Britain. Even in December’s grim election, the party performed well in cities as different from each other – in their degrees of wealth and poverty, their positions in the country, and their sense of identity – as Liverpool and London, Birmingham and Newcastle, Leicester and Bristol. In recent decades, these and other English cities have become Labour strongholds – often more so than the party’s “traditional” heartlands. Yet in the debate about the party’s future so far, the cities have barely figured.

In one, limited sense, this omission is reasonable. Since the party isn’t in obvious crisis in these places, you could argue that they don’t need to be the focus of any programme of renewal. But successful political parties watch and draw lessons from the way the world is changing – and Britain’s cities have often been where new political and social forces first emerge, from multiculturalism to feminism and environmentalism. When Labour is influenced by such movements, it gains fresh energy. Cities are where the party has adapted best to the deep shifts and sudden disruptions of the modern world.

‘Between Tony Blair’s first election victory in 1997 (above) and his final one in 2005, Labour lost four million voters.’ Photograph: Max Nash/AP

Yet only a few decades ago, many urban constituencies seemed vulnerable territory for Labour. They had some similar social and political characteristics to the left-behind towns now. Even Islington. When Jeremy Corbyn became the MP for its scruffier northern portion in 1983, his constituency was largely white and working class. Labour had held it since the 1930s, but often only with a modest majority, which had shrunk to under 5,000 in 1979. The area had high unemployment, poor housing, and a local Labour party that was seen as complacent and ineffective. Many of its members and voters were defecting to the newly formed SDP. It seemed possible Labour would soon lose the seat altogether.

Instead, the opposite happened. As Islington North gentrified, it attracted waves of incomers, from bankers to migrant businessmen to refugees – few of them “traditional” Labour voters, and Corbyn got to know them and was often influenced by them. Amid Labour’s crushing defeat last month, his majority was 26,188.

The point here is not to stand up for the beleaguered party leader, but that a plan to revive Labour beyond the cities – without which it won’t win power again – must fit the world as it is, rather than as it used to be.

Last month, the Centre for Towns, a thinktank co-founded by the Labour leadership candidate and Wigan MP, Lisa Nandy, published revealing but little-noticed research about a dozen of the northern seats lost by Labour to the Conservatives last month. Between 1981 and 2011, all of them experienced huge decreases in the proportion of their young residents, and similar increases in the proportion of retired people. In County Durham, Bishop Auckland’s 18- to 24-year-olds went down by 25%, and its over-65s went up by almost 35%. Last month, it was taken by the Tories after more than 80 years of Labour control.

Since the early 1980s, the narrowing of economic opportunities in much of the north and their widening in the south has transformed the electorate in many northern seats: effectively shifting it to the right, given the strong Labour and Tory biases, respectively, of the young and old. The loss of many of these seats last month ought not to have been such a surprise; it was decades in the making.

Back in the 90s, New Labour understood that the party’s old heartlands were weakening. In 2007, Tony Blair’s electoral strategist Philip Gould wrote that Blairism had been, and should continue to be, “rooted not in Labour’s traditional industrial heartlands but in the sprawling suburbs of an emerging middle class”.

For a while, New Labour skilfully kept both parts of the country happy, generously distributing cabinet jobs and public works to northern constituencies, while tailoring its economic and tax policies to the needs of more prosperous southerners. Yet, underneath, New Labour operated on the assumption that the party’s “traditional” voters had “nowhere else to go”, as Blair’s spin doctors often put it with a certain smugness. That assumption was mistaken; but fortunately for Blair, instead of voting Tory, as many of them did last month, during the Blair years they mainly just didn’t vote (between his first election victory in 1997 and his final one in 2005, Labour lost four million voters).

It won’t be easy for Labour to find a politics that satisfies both homeowning pensioners living in depopulating towns and villages, and precariously employed young renters living in overcrowded cities. In their assets, in their attitudes, in their economic experiences, their lives are ever more different. Meanwhile, under Boris Johnson the Tories seem more interested than they have been for decades in listening to the Britain beyond their own heartlands in southern England.

Labour could wait for that relationship to go wrong. But there is no guarantee that voters will then return to Labour. The Brexit party, or some other, yet-to-be-formed vehicle for nationalism, or regional pride, or nostalgia, may appeal to an ageing electorate more.

Labour will probably have to accept that some of its old “heartlands” are gone for good. In the cities, and in growing southern towns such as Swindon, which New Labour won and the party has since lost, Labour will have to build new ones.

• Andy Beckett is a Guardian columnist