Britain's new Prime Minister Keir Starmer (left) and his wife Victoria Starmer wave to the media on the steps of 10 Downing Street in London on Friday. (EPA-Yonhap)

Keir Starmer set to work as Britain's new leader Friday, speaking with other world leaders and appointing his ministerial team after his Labor party's landslide general election victory ended 14 years of Conservative rule.

Starmer named Rachel Reeves the UK's first woman finance minister and appointed David Lammy as foreign secretary following his election win to become center-left Labor's first prime minister since Gordon Brown in 2010.

Flag-waving crowds of cheering Labor activists lined Downing Street as Starmer pledged to "rebuild" the UK after head of state King Charles III invited him to form a government during a meeting at Buckingham Palace.

"Now, our country has voted decisively for change, for national renewal and a return of politics to public service," the 61-year-old said in his first speech as PM.

"The work of change begins immediately, but have no doubt, we will rebuild Britain."

Within hours, Starmer held calls with US President Joe Biden and Ukrainian President Volodymyr Zelensky, reaffirming London's "unwavering" support for Kyiv's war against invading Russian forces.

"I look forward to our shared work in support of freedom and democracy around the world, and to further strengthening the special relationship between our two countries," Biden said on X.

Earlier, a somber Rishi Sunak conceded defeat during a torrid night for his Conservatives that claimed the scalps of at least 12 of his senior cabinet colleagues -- and his predecessor Liz Truss.

Her disastrous 49-day tenure effectively sealed the Tories' fate with the public two years ago, when her unfunded tax cuts spooked markets and crashed the pound.

Before leaving Downing Street for the final time as prime minister, Sunak said "sorry" to the public and revealed that he would step down as Tory leader once formal arrangements for a successor are in place.

The Tories' worst previous election result was 156 seats in 1906. Former leader William Hague told Times Radio this was "a catastrophic result in historic terms." By late Friday, Labour had won 412 constituencies in the 650-seat House of Commons -- with only one result left to declare -- giving it a majority of 174.

The Tories won just 121 -- a record low -- with the right-wing vote apparently spliced by Nigel Farage's anti-immigration Reform UK party, which picked up five seats. In another boost for the centrists, the smaller opposition Liberal Democrats ousted the Scottish National Party as the third-biggest party.

The results buck a trend among Britain's closest Western allies, with the far-right in France eyeing power and Donald Trump looking set for a return in the United States.

Congratulations came in from European leaders, including Germany's Chancellor Olaf Scholz, who said Starmer would be a "very good, very successful" prime minister.

Zelensky said the two countries would "continue to be reliable allies through thick and thin."

Ex-US president Donald Trump congratulated his admirer Farage on winning election to the UK parliament at his eighth attempt, but noticeably neglected to mention Starmer.

Outside London's busy Waterloo station, 49-year-old engagement officer Ramsey Sargent called it a "momentous election."

"It has been very rocky over the last few months and years. I'm really excited to see what happens next," he told AFP.

Tim Bale, politics professor at Queen Mary, University of London, said the Conservatives' drubbing was "not as catastrophic as some were predicting" and that the Tories would now need to decide how best to fight back.

Brexit champion Farage has made no secret of his aim to take over the party.

"There is a massive gap on the center-right of British politics and my job is to fill it," he said after a comfortable win in Clacton, eastern England. Labor’s resurgence is a stunning turnaround from five years ago, when hard-left former leader Jeremy Corbyn took the party to its worst defeat since 1935 in an election dominated by Brexit. Starmer took over in early 2020 and set about moving the party back to the center, purging the infighting and anti-Semitism that cost it support. Opinion polls consistently put Labor 20 points ahead of the Tories since Truss's resignation, giving an air of inevitability about a labor win -- the first since Tony Blair in 2005. But as the count neared the end, the gap was around 11 percent, with Labor looking set to win fewer votes than it did in 2019, partly reflecting a lower turnout.

Starmer faces a daunting in-tray, from anemic economic growth to overstretched and underfunded public services and households squeezed financially. He has promised a return of political integrity, after a chaotic period of five Tory prime ministers in 14 years, scandal and sleaze. (AFP)