Rishi Sunak has suffered a heavy defeat in his first electoral test as Prime Minister.
The Conservatives slumped to just 22.4% of the vote as voters headed to the ballot box in the City of Chester by-election.
Labour held the seat with an increased majority of 10,974, as Samantha Dixon was elected to Westminster.
The contest was triggered by the resignation of Labour’s Christian Matheson, who resigned after complaints of serious sexual misconduct were upheld by a parliamentary watchdog.
Matheson, who has denied the allegations against him, was facing a four-week suspension and was asked to resign by Labour before he quit.
In the vote on Thursday, Labour’s Dixon defeated Conservative candidate Liz Wardlaw.
Labour hailed the victory as sending a “clear message” to Sunak and his administration.
In a speech after winning the seat, Dixon accused the Conservatives of having “wreaked havoc” on the economy.
She also insisted that Sunak’s government has “no ideas, no plan” to address the issues facing the country.
“Tonight, the people of Chester sent a clear message to the Conservative government,” she said.
“They have said unreservedly that Rishi Sunak’s Conservatives no longer have a mandate to govern.
“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.
“It’s time for a general election and it’s time for a Labour government.”