“My government will make you believe again,” Starmer said as supporters cheered him on. “The work for change begins immediately. We will rebuild Britain. …. Brick by brick we will rebuild the infrastructure of opportunity.”

The Conservative Party suffered its worst election defeat, winning just over 120 seats. Outgoing prime minister Rishi Sunak, speaking before meeting King Charles to formally resign, said he intended to step down as leader of the party once the succession process is in place.

Sunak, who led a lacklustre six-week campaign, conceded the public had sent a clear signal the government must change. “I have heard your anger, disappointment and I take responsibility for this loss,” he said.

Voters punished the Tories for a cost-of-living crisis, failing public services, and a series of scandals. Since winning a landslide election under Boris Johnson in 2019, the party has presided over Britain’s departure from the European Union, and response to the pandemic and policy on the war in Ukraine.

The country also suffered economic turmoil during the ill-fated six-week term of prime minister Liz Truss in 2022, who was one of many high-profile conservative MPs to lose her seat.

Eleven cabinet ministers were defeated, a record, including Defence Secretary Grant Shapps and Commons Leader Penny Mordaunt, who had been seen as a potential party leader.

Sunak described Starmer as a “decent, public-spirited man who I respect” and said the new prime minister deserved understanding “as he grapples with this most demanding of jobs in an increasingly unstable world”.

Congratulations for Starmer poured in from state leaders.

Australian Prime Minister Anthony Albanese said in a post on X that he looked forward to “working constructively” with the new British government. New Zealand Prime Minister Christopher Luxon also took to X to congratulate Starmer, writing: “New Zealand and the UK are great friends and can do so much together”.

Indian Prime Minister Narendra Modi wished Starmer “heartiest congratulations and best wishes”, describing his victory as “remarkable”.

Labour’s majority of at least 174 seats is just short of that secured by Tony Blair in his thumping 1997 election win. It represents an extraordinary turnaround in the Labour Party’s fortunes after suffering its worst defeat in 84 years in the last general election, in 2019.

But Starmer, who moved the left-wing party to the centre after becoming leader in 2020, said the mandate “comes with great responsibility”. He told his supporters: “I don’t promise you it will be easy. Changing a country is not like flicking a switch. It’s hard work, patient work, determined work”.

While the Labour win is convincing in terms of the seats won under Britain’s first-past the-post system, there are warnings for the new leader.

Labour’s share of the vote, at only around 34 per cent, is historically low. The election was marked by tight results in many constituencies and strong performances by resurgent smaller parties.

The Liberal Democrats celebrated the winning of a record 71 seats. The right-wing Reform Party won around 14 per cent of the vote and claimed four seats, drawing voters away from the Conservatives, with leader Nigel Farage, winning at the eighth attempt.

Farage vowed to forge a mass movement. He said: “This Labour government will be in trouble very, very quickly and we will now be targeting Labour votes. We are coming for Labour. This is just the first step of something that is going to stun all of you”. The Green Party secured four seats and independents, six.

Labour, meanwhile, made big gains in Scotland, where the Scottish National Party, which supports independence from the UK, lost 38 seats. The Conservatives did not win a single seat in Wales.

Starmer will have a long to-do list as he seeks to make good on promises to fuel economic growth and improve services, including the struggling National Health Service, while raising the standard of living, and tackling global issues from climate change to the conflicts in Gaza and Ukraine.