Labour has won a convincing victory in the City of Chester by-election and delivered a blow to Rishi Sunak in his first electoral test as Prime Minister.
Deputy leader Angela Rayner said Mr Sunak had "failed" and the Tories had taken a "pelting" after new MP Samantha Dixon increased Labour's majority by more than 4,000 votes.
Ms Dixon secured a 10,974 vote majority in a contest triggered by the resignation of Labour MP Christian Matheson, who quit after complaints of "serious sexual misconduct" were upheld by a parliamentary watchdog.
Labour won 61% of the vote share in a 13.76% swing from the Tories, the biggest majority the party has won in the swing seat, which has been red since 2015.
The Tories had their worst result in City of Chester since 1832, with 22.4% of the vote, in the party's first defeat in a by-election since Boris Johnson was ousted and Liz Truss's crisis-ridden stint in No10.
Turnout was 41.2%, with a total of 28,541 votes cast.
On a victory lap this morning, Ms Rayner said the people of Chester delivered a "huge message" to the Government on their desire for change.
"He's [Rishi Sunak] failed that test, it's very clear that he doesn't have the mandate to govern and that people want a general election and they want change," she told broadcasters.
"It is clear that this was Rishi Sunak's first test as Prime Minister, and it was his worst defeat since 1832 here.
"It's pretty clear that the Conservatives... their branding has absolutely took a pelting."
Keir Starmer said it was a "very, very good result" for Labour.
Speaking on a visit to Glasgow, the Labour leader said: "The Government is worn out, tired, has crashed the economy. And the verdict was very, very clearly given.
"I think that's a clear message to Prime Minister Rishi Sunak that people are fed up and they want to change.
"There's this strong sense now that the Government has run out of road, run out of ideas, hasn't got a mandate, and it's time for change."
Polling guru Professor Sir John Curtice said voters had sent a warning to Mr Sunak that he had "quite a lot of work to do" to get to a point where the Tories could win the next election.
Prof Curtice said it was the best performance for Labour in a by-election since David Cameron was Tory leader.
While he cautioned about comparing by-election results to a national poll, he said a swing of this size would deliver Keir Starmer a majority at a general election
"Labour are in a stronger position than they have ever been in the last 10, 12 years and the performance is "consistent" with what happened the last time we had a Parliament that ended in Tory defeat," he told the BBC.
Lord Robert Hayward, a Tory peer and elections analyst, said there were "no shocks" for Labour and there is "no question" the Tories have a "real challenge on their hands".
"I think, generally as expected, no shocks but definite satisfaction for the Labour Party," he told Sky News.
"Rishi comes across to the public at large as managerial," he said. "His ratings are way ahead of the Tory party's. His ratings which will worry the Labour Party, are on a par with Keir Starmer, depending on which poll you actually look at.
"There are some indications that there are opportunities there for the Tory party. But Rishi has to convince the public at large that he can manage out of this crisis, whichever crisis one's looking at - and there's a lot of them."
Speaking after the result, Ms Dixon said: "I think I have been in receipt of a very strong message from the voters of Chester that they want the Conservative cost-of-living crisis tackled immediately.
"I don't think they believe that the Conservatives have the answers, I think they think it's Labour's turn now."
She described Chester as a "bellwether constituency" and said the result was "really, really encouraging".
"People in Chester and across our country are really worried," Ms Dixon said.
"Worried about losing their homes because they can't afford the mortgage repayments or the rent, worried about whether they can put the heating on, worried about whether they can put food on the table for their families.
"This is the cost of 12 years of Conservative Government. The Government which has wreaked havoc with our economy, destroyed our public services and betrayed the people who put their trust in them at the last general election."
Ms Dixon claimed that the Tories are now on "borrowed time".
"They have said unreservedly that Rishi Sunak's Conservatives no longer have a mandate to govern," she continued.
"His Government has broken the promise that each generation should do better than the last. His Government has no ideas, no plan to address the big issues facing our country. His Government is on borrowed time and people want to change."
Shadow Work and Pensions Minister Alison McGovern said: "The people of Chester have sent a clear message to Rishi Sunak's Conservative government: They are fed up of Tory rule and want the change Labour offers.
"After the Tories crashed our economy, it's clear that only Labour can be trusted to help families across the country make ends meet."
The result is the latest by-election defeat suffered by the Conservatives.
The last two by-elections, held in June, were a disaster for the Tories, with Labour snatching the Red Wall seat of Wakefield and the Liberal Democrats scoring an upset in Tiverton and Honiton, in Devon.
It marks Mr Sunak's first electoral test since becoming Prime Minister in October, leaving him to pick up the pieces after Liz Truss trashed the economy in her 45-day stint in No10.
Labour has been ahead in the polls after months of Tory infighting and chaos,
