On Monday, Keir Starmer announced he would resign as prime minister after two years in seat—something that may seem short for leaders of some countries, but for the U.K., ranks as one of the longer tenures in recent years. Nominations for a successor will open next month, and a next party leader is likely to be decided soon after, at which point Starmer’s resignation will mark the end of a chaotic period filled with political whiplash that saw his Labour Party suffer devastating losses in local elections last month.

Starmer’s resignation paves the way to the premiership for Andy Burnham, the former mayor of Greater Manchester. If chosen by Labour, Burnham will become the U.K.’s seventh prime minister to have held office in the decade since Britons voted on the country’s new trajectory. 

The years since have been a time of volatility unmatched in the U.K.’s recent political history, compounded by economic malaise and deep-rooted societal changes that will likely hold repercussions deep into the next decade and beyond.

With Starmer’s announcement, the outgoing prime minister brought a fittingly turbulent end to a chaotic decade, one that began with a similar strain of political upheaval.

Whiplash, by the numbers

Six prime ministers have taken office at 10 Downing Street since the referendum, none of whom have lasted long enough to bury the political instability Brexit unleashed.

David Cameron, who called the Brexit campaign an act of “economic self-harm” and campaigned voraciously against it, was forced to quit his post the morning after losing. Theresa May then spent three years in office trying and failing to pass a Brexit deal that made no one happy, and was eventually voted down by the House of Commons in the largest loss for a sitting government in the country’s modern history. 

Boris Johnson campaigned with a clear promise: to “get Brexit done.” His supporters rewarded him with a landslide victory, then held their tongues as the Conservative leader bowed to rancorous calls to resign amid the Partygate scandal after three years in office. His successor Liz Truss lasted 49 days—a tenure memorably outlasted by a supermarket lettuce. Rishi Sunak steadied things just long enough to preside over the Conservatives’ worst electoral defeat in parliamentary history, yielding to Starmer in 2024. 

And now Starmer himself is out less than two years into a five-year mandate, his Labour government undone by a local-election drubbing and a right-wing populist rise that has scrambled the country’s two-party map.

Each departure was tainted by its own cocktail mix of political poison: failed attempts to get Brexit over the line, scandals, economic headwinds, or landslide defeats. The past 10 years have hardly left U.K. politics on more stable footing compared with the day Britons voted to leave, though even if voters might have grown accustomed to the revolving door at Downing Street, the economic repercussions of the country’s volatility are just beginning to be laid bare. 

A demographic cliff arrives ahead of schedule

While Westminster cycled through leaders, Britain’s underlying population accelerated into a slide that might prove almost impossible to reverse. 

In April, the Office for National Statistics (ONS) published its latest population projections, which forecast a demographic turning point occurring between 2025 and 2026. Last year, according to the ONS, was the last time births in the country exceeded deaths. Sometime in mid-2026, deaths will outnumber births, and keep doing so for the foreseeable future. Absent enough immigration to replace the decline in natural births, the U.K. now faces certain population decline in the not-too-distant future. 

Between 2024 and 2034, the ONS projects 6.4 million births against 6.85 million deaths—a natural shortfall of roughly 450,000 people over the coming decade or so. Beginning in 2026, net migration is the only thing keeping the population growing at all, and even that is no longer a certainty. The latest ONS projections forecast the U.K.’s population will grow by 1.7 million people by 2034, almost half the increase estimated last year, largely owing to declining net migration.

“Our latest projections indicate slower population growth than previously projected,” James Robards, head of population projections at the ONS, said in statements reported by the Guardian. “This is mainly due to lower migration assumptions—reflective of the recent steep fall in net migration—and lower fertility assumptions.”

Other countries are facing a similar demographic cliff, including the U.S., where population growth has slowed lately owing to falling birth rates and declining net migration. In the U.K., as in the U.S., population size is projected to peak around the mid-2050s before declining.

But the economic consequences will be felt far earlier. The number of Britons of pensionable age is set to grow by 1.8 million over the next decade, even as the number of children falls by 1.6 million, shrinking the future tax base needed to support a larger pension and health care bill. 

It’s a fiscal squeeze with no easy political fix, regardless of who might be sitting in Downing Street.

The Brexit bill comes due

If the demographic trend is slow-moving and largely independent of the referendum, the economic one is not. The decision to leave the EU and rewrite several tomes’ worth of trade and industrial policy has taken a comprehensive toll on the British economy, according to a working paper published last week by the National Bureau of Economic Research.

Over the past decade, Brexit has cost the U.K. economy between 6% and 8% of its GDP, the authors found from an analysis of Bank of England data. In those 10 years, investment fell 12% to 13%, employment decreased 3% to 4%, and productivity also declined between 3% and 4%.

Those losses have compounded over time and are directly tied to the political instability that has plagued the U.K. since the vote. The authors estimated that around half of GDP loss was attributable to the years of elevated policy uncertainty. Brexit generated unease that firms rated as one of their top three concerns for nearly five years after the vote, only moderating somewhat in 2021 once a new EU trade deal took effect. The remainder of the lost growth came down to higher costs imposed by more cumbersome trade restrictions.

Ten years out from the day of that historic vote, the steps of No. 10 are increasingly well-trodden, while the U.K. has become saddled with a population now tilted toward old age and an economy that’s smaller than it would otherwise have been. The vote may have taken place over a single day, but its bill is still adding up.