CENTRAL Birmingham is buzzing. The fine square in Brindleyplace is lined with snazzy restaurants, and after 6pm, smartly dressed office workers. (“Every year there are more of them,” says a waiter.) In 2003 the city got a globby new branch of Selfridges, a posh London department store (see picture), and in 2011 its first craft beer bar took over a former post office. Behind the redbrick factory facades of nearby Bradford Street, the yuppies are also taking over, quietly occupying new flats within.

Many of these go-getters are former Londoners. According to the Office of National Statistics, a record number of 30- to 39-year-olds left the capital in the year to June 2013: a net outflow of nearly 22,000 (and a 25% increase on 2010). They have settled in Birmingham, which attracted the largest number, as well as Manchester, Bristol and Oxford. London has long shed people in their 30s. Mainly they want bigger, cheaper living-space for their children. London’s soaring house prices have exacerbated the trend: the city’s average property price rose by 19% in the past year. It now stands at £402,800 – in Birmingham it is £133,700.

Those fleeing London are often moving jobs, too. Statistics from the Institute for Fiscal Studies suggest the fraction of London’s workers aged 30-39 who commute has not increased in the past few years. Centre for Cities, a think-tank, points out that they are also prepared to take a pay cut. In Milton Keynes, a town just north of the capital, the average wage is £28,600, while London’s is £33,000. Yet the average cost of a house in Milton Keynes (£209,600) is less than half London’s, so despite a 13% pay cut, those headed for Milton Keynes are likely to enjoy a higher disposable income. It is not just a lifestyle choice: public-sector workers’ “London allowances” are no longer sufficient, says Alan Manning of the London School of Economics.

As people move out of the capital, earning smaller amounts and spending even less, this will hit the country’s GDP. A 2014 study by economist Enrico Moretti at the University of California, Berkeley, showed that a lack of affordable houses in America’s strongest performing cities between 1964 and 2009 cost national output 13%.

The trend is not without advantages, however. Priced-out Londoners are spreading wealth around the country—investing this hard-won disposable income in jazzing up cities like Birmingham and Manchester. (These places are also acquiring London’s problems: Birmingham will need 84,000 houses over the next 20 years to keep up with current demand; the average house price rose 10% during 2013.) As policymakers scheme to make Britain less London-centric (see article), the capital’s overheated property market is doing the job for them.