WHEN Sheffield Town Hall opened in 1897, it was a symbol of pride in a city on a Victorian growth spurt. Now it stands lost in an urban wasteland. A 13-shop stretch along a nearby high street includes six empty buildings, five temporary shops, and a clothing store selling everything for under £10 ($16). A mere 15-minute tram ride out of the city, though, reveals a different scene—lit-up office blocks where workers jog on treadmills in ground-floor gyms, beside a buzzing shopping centre called Meadowhall. At 5.30pm the ground floor of Debenhams, a department store in the mall, is more densely populated than Sheffield’s entire central high street.

Britain’s cities are falling either side of a divide. A few—mainly the big ones—are growing at the core and faltering towards the edge. London’s highest levels of unemployment used to be in the inner city borough of Tower Hamlets, now they’re in the suburbs of Greater London: Barking and Dagenham and Newham. Between 1998 and 2008, Birmingham’s private sector job numbers stayed flat but moved inward (they grew 27% at the centre). But most of Britain’s towns and cities—places like Luton, Wakefield, Sunderland—are doing precisely the opposite: the action is on the outskirts, the centres ever more deserted. Fully 22% of Sheffield’s central business units stand empty; in 2011 McDonald’s left Rochdale centre (though not its edges). If London is getting more like Paris, these towns increasingly resemble America’s sprawling cities, such as Cleveland and Houston.

Why? One explanation is that agglomeration effects—the economies of scale when businesses cluster—are getting more important as the economy shifts towards high-tech and finance. Information-sharing and networking, which benefit such industries, work best over a small area. City centres that managed to reach a certain density of these businesses will now continue to attract more of them; those that did not will thin out, falling prey to a range of powerful economic and social forces.

A major force hollowing out places like Sheffield is the existence of out-of-town shopping centres and business parks built in the 1980s and 1990s: cities with weaker centres have not been able to withstand them. (Meadowhall seems to have done not only for Sheffield’s centre, but nearby Rotherham’s as well.) Smaller towns often come with thinner green belts, inviting expansion (bigger cities must develop their centres instead). Another reason is increased mobility, which means big cities can drain skilled employees from surrounding areas. Manchester and Liverpool absorb 20% of the North-West’s service industry jobs. Smaller cities are left with industries like manufacturing and transport, which prefer to be on the edge, close to motorways. The growth of online shopping also affects the high street.

Councils in hollowed-out towns are unhappy with the trend: the high street has always been a metric for how well a city is doing, and boarded up shopfronts look bad. There is barely a decentralising city without plans to reverse it; Sheffield has invested £17m in a large indoor market in the centre. The central government in 2012 allocated £2.3m to “Portas pilots”—struggling town centres identified by Mary Portas, a retail consultant —and a further £10m to a High Street Innovation Fund.

This is all likely to be a waste of money. As fast as high street tax-breaks are granted, out-of-town shopping centres expand, and transport links to the neighbouring vampire metropolis are improved. Communities secretary, Eric Pickles, has just approved a 43,200 square metre (465,000 square foot) retail park in Rushden. “It will kill Northampton”, says Matthew Hopkinson of The Local Data Company, a research firm. America has plenty of similar plans to save city centres, but places like Phoenix have continued to suburbanise.

The inability to recentralise does not preclude success, however. Between 1998 and 2008 Wakefield was one of Britain’s stronger private-sector job creators, and those jobs were almost all created in the suburbs. Cambridge and York, which encourage expansion in suburban business parks to preserve their historic centres, are growing. Deserted centres also have solutions which do not involve rejuvenating the high street: giving the space over to housing, for example, which should also boost whatever shops are left. Leicester is turning it into student accommodation. Town halls are no longer in the thick of the action, says Professor Tony Travers of the London School of Economics, but that is “not the worst thing in the world”.