Labour has won the Chester by-election – the first public vote since Boris Johnson and Liz Truss were ousted from Number 10.
Samantha Dixon retained the seat for her party with 17,309 votes – a 61% share and nearly 11,000 more than the Conservative candidate.
Labour was expected to win but the margin was bigger than in 2019, when its majority was 6,164 – or just under 50%.
It represents a 13.8% swing from Tory to Labour, the sixth largest between the parties at a by-election since 1945, and more than the 12.7% in Wakefield in June.
It is also the worst result for the Conservatives in Chester since 1832, with candidate Liz Wardlaw getting 6,335 votes, or 22.4%.
Ms Dixon told Sky News the result was a “resounding mandate” for Labour, and in her victory speech said the Tories were “on borrowed time and people want to change”.
Sky’s chief political correspondent, Jon Craig, described it as a “crushing defeat” for the Tories and “ominous” for the party’s chances at the next election.
However, he said it would be harsh to personally blame new prime minister Rishi Sunak for the result.
It comes after a big disappointment for the Conservatives in two summer by-elections which saw Labour snatch Wakefield and the Lib Dems secure a historic victory in Tiverton and Honiton.
The Chester contest was triggered by the resignation of Labour MP Chris Matheson, who was suspended in October after two allegations of sexual misconduct from a former staff member were upheld.
The result follows a slump in opinion polls for the Conservatives after a raft of reshuffles in their top ranks.
The party saw a small bounce in their numbers after Rishi Sunak entered Downing Street last month – the third Tory leader this year – but the Tories are still regularly polling behind Sir Keir Starmer’s Labour Party.
This is the first of two by-elections this month, with another taking place on 15 December in Stretford and Urmston, Greater Manchester.
That vote was called after Labour’s former shadow education secretary, Kate Green, announced she was standing down to become deputy mayor of Manchester.