Labour Party leader Keir Starmer shakes hands with supporters Friday at the Tate Modern in London. Kin Cheung/Associated Press

LONDON — Britain’s new prime minister, Keir Starmer, vowed Friday to reverse the hopelessness that grew over 14 years of Conservative rule and said he would lead an urgent mission of national renewal after his Labour Party’s landslide victory.

It will be a tall order.

Rising poverty, crumbling infrastructure, a lagging economy and an overstretched National Health Service contributed to widespread dissatisfaction and gripes about “broken Britain.” The resulting defeat was the worst ever for Conservatives.

“Have no doubt that we will rebuild Britain,” Starmer said in his first official remarks as supporters cheered and waved union jack flags outside No. 10 Downing St. “Brick by brick, we will rebuild the infrastructure of opportunity.”

Starmer said it would take time but pledged that his government would get the National Health Service “back on its feet,” secure the U.K.’s borders, improve public safety and cut electric bills while relying on homegrown clean energy.

Among those who gathered to watch the government change was David McKeever, who said Starmer needed to quickly provide the details of his plans, which were often lacking during the campaign.

“From today onwards, Keir Starmer is going to have to come up with some actual policies and implement them,’’ McKeever said. “We’ll know in time what we’re dealing with. But, yeah, clearly the Tories had set such a monumentally low bar you could have fallen over it.”

Before Starmer arrived at No. 10, his predecessor, Rishi Sunak, bid farewell in a reflective speech from the same spot where he called for the snap election that led to his ouster.

“I have heard your anger, your disappointment, and I take responsibility for this loss,” Sunak said. “To all the Conservative candidates and campaigners who worked tirelessly but without success, I’m sorry that we could not deliver what your efforts deserved.”

Sunak’s party – which has been wracked by scandals, turbulent leadership changes and global problems – suffered the biggest defeat in its two-century history.

With results tallied for all but one constituency, Labour had won 412 seats in the 650-seat House of Commons. The Conservatives had only 121 – down from 365 seats in 2019. The drubbing surpassed even the 1906 election, in which they won just 156 seats.

The Tory reign was marked by Britain’s messy divorce from the European Union, followed by the COVID-19 pandemic and Russia’s invasion of Ukraine, all of which battered the economy.

When Sunak took over in October 2022, he was the third prime minister in less than two months and set out to bring stability to a party in crisis.

Widespread anger over parties thrown by then-Prime Minister Boris Johnson’s staff, in violation of his own lockdown rules, led to his departure. His successor, Liz Truss, left office in a record 49 days after shaking the economy with a package of drastic tax cuts.

On Thursday, Truss narrowly lost her seat to Labour, becoming the first former prime minister in nearly 90 years to lose their seat in Parliament. She was one of a slew of senior Tories kicked out in a stark electoral reckoning.

Britain’s King Charles III, right, shakes hands with Keir Starmer as he invited the Labour Party leader to become prime minister and to form a new government Friday in London. Yui Mok/Pool photo via AP

Starmer began appointing government ministers who would be responsible for helping to turn Britain’s problems around. He announced that Rachel Reeves, a former Bank of England economist, would be the Treasury chief, making her the first woman to hold the job.

The massive victory will bring big challenges for Starmer. He acknowledged as much in referring to the “gap between the sacrifices made by people and the service they receive from politicians,” which he said led to “weariness in the heart of a nation, a draining away of the hope, the spirit, the belief in a better future.”

Tim Bale, a politics professor at Queen Mary University of London, said whether Starmer can fix public services fast enough to satisfy expectations is a question.

“The National Health Service is in crisis,” Bale said. “It’s going to take quite a lot of money to restore its fortunes. The question is, where Labour will get that money from and how quickly it can manage to do it.”

In a sign of the volatile public mood and anger at the system, the incoming Parliament will be more fractured and ideologically diverse than any in years.

Smaller parties picked up millions of votes, including the centrist Liberal Democrats, who captured 71 seats – up by 60 from the last election. The left-wing Green Party won four seats, up from just one.

One of the biggest losers was the Scottish National Party, which held most of Scotland’s 57 seats before the election but looked set to lose all but a handful, mostly to Labour.

While the overall result appeared to buck recent rightward electoral shifts in Europe, including in France and Italy, many of those same populist undercurrents also flow in Britain.

Reform UK, the party of Nigel Farage, who roiled the race with his party’s anti-immigrant “take our country back” sentiment, won five seats. That included one in the seaside town of Clacton-on-Sea, where Farage at last secured a place in Parliament on his eighth attempt.

Reform, however, actually had a larger share of the total vote than the Liberal Democrats and undercut support for the Conservatives and even grabbed some voters from Labour.

Outgoing British Prime Minister Rishi Sunak leaves Conservative Campaign Headquarters in London on Friday. Thomas Krych/Associated Press

However, Reform failed to gain as many seats because its votes were not as efficiently distributed as the centrist Liberal Democrats. In Britain’s electoral system, the candidate with the most votes in each constituency wins.

Labour’s path to victory was largely a result of a cautious, safety-first campaign without making mistakes. Starmer may have lacked charisma, but his pledges to improve the economy, invest in infrastructure and fix broken social services resonated. The party also won business backing, including endorsements from traditionally conservative newspapers such as Rupert Murdoch’s The Sun tabloid, which praised Starmer for “dragging his party back to the center ground of British politics.”

The Conservatives, in comparison, were plagued with missteps, including Sunak’s decision to bail out early on commemorations marking the 80th anniversary of the D-Day invasion in France. The campaign got off to an inauspicious start when Sunak stood under a downpour outside No. 10 in May to set the election date.

Six weeks later, on a day marked by occasional rain reminiscent of his election announcement, Sunak stood there to bid adieu and offered his best wishes to his “decent, public-spirited” successor, despite their disagreements in the campaign. He said he would also step down from his Conservative leadership role.

Two hours later, Starmer stood in the same spot. He thanked Sunak for his dedication and noted he was the first British prime minister of Asian descent.

He then asked both those who supported him and those who didn’t to join him in the mission of national renewal.

“Our work is urgent,” he said. “And we begin it today.”

Associated Press journalists Kwiyeon Ha, Danica Kirka and Pan Pylas contributed to this report.