Labour has easily won the by-election in Chester, a defeat for Rishi Sunak in his first test at the ballot box since becoming prime minister.

Samantha Dixon, Labour’s candidate, won with a majority of 10,974 over Tory Liz Wardlaw.

Labour had been widely expected to hold on to the seat but the size of the win is a boost for Keir Starmer.

The by-election was called after the incumbent Labour MP Christian Matheson resigned after complaints – which he denied – of “serious sexual misconduct”.

It was the first by-election since Boris Johnson was ousted and the market chaos that defined Liz Truss’s short stint in No.10.

Labour won the seat in 2019 with a majority of 6,164. The Conservatives last won it at the general election in 2010 which saw David Cameron become PM.

The result will be seen as further evidence that the Conservatives are on course to lose the next general election, due in 2024.

A YouGov poll released on Thursday, as voters went to the polls in Chester, showed Labour hold a 25 point lead nationally over the Conservatives.

In a victory speech after the result was announced, Dixon said: “People in Chester and across our country are really worried.

“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.”

The result is the latest by-election defeat suffered by the Conservatives.

The last two by-elections, which took place on the same day in June, were a disaster for the Tories, with Labour snatching Wakefield and the Liberal Democrats securing a historic victory in Tiverton and Honiton.

The result, which comes just over a month into Sunak’s tenure as prime minister, is unlikely to be seen as a referendum on his leadership.

But it nonetheless comes as a blow to the party, which is facing an uphill battle to remain in office at the next nationwide poll.

The country is facing a gloomy outlook, after chancellor Jeremy Hunt’s autumn statement last month ushered in a fresh round of belt-tightening in the public finances as the UK heads into a recession and soaring inflation squeezes incomes.

With many households struggling with rising energy bills, rail strikes and a planned walk-out by nurses also threaten to cause severe disruption in the run up to Christmas.