Labour has suffered a historic defeat at a crucial by-election in one of its northern heartlands, raising fresh doubts over Jeremy Corbyn’s leadership of the party.

The Conservative victory in Copeland marks the first time an opposition party has been defeated by the Government at a British by-election in 35 years. The scenic Cumbrian seat – and its predecessor Whitehaven – has been represented by Labour since 1935.

Trudy Harrison, the Conservative candidate, defeated Labour’s Gillian Troughton, a volunteer for St John Ambulance, by 2,147 votes. Labour secured a 5,179 majority at the general election in 2015.

Labour’s candidate Gareth Snell clearly defeated Paul Nuttall, the embattled Ukip leader, by 2,620 votes, calling into question the ability of the party to capitalise on the result of the Brexit referendum last year.

Shortly after the results were announced, the Labour leader said the victory in Stoke was a “decisive rejection” of Ukip’s “politics of division and dishonesty”. But, he added: “Our message was not enough to win through in Copeland.”

He said: “In both campaigns, Labour listened to thousands of voters on the doorstep. Both constituencies, like so many in Britain, have been let down by the political establishment.

“To win power to rebuild and transform Britain, Labour will go further to reconnect with voters, and break with the failed political consensus."

Downing Street will undoubtedly be jubilant at the historic result, especially after Theresa May decided to visit the party’s candidate in the constituency just last week.

Trudy Harrison arrives with her husband Keith ahead of the announcement of the results of the Copeland by-election (Getty)

The last time a governing party took a seat from the opposition at a by-election was in 1982 when the Labour MP for Mitcham & Morden defected to the SDP.

The humiliating defeat in Copeland is likely to renew questions over Mr Corbyn’s leadership of Labour. With the party trailing in the nationwide opinion polls – the latest placed Labour 18 points behind Ms May’s Conservatives – the dismal result will be used by his critics to say Mr Corbyn has little chance of securing inroads at the next general election.

Copeland is heavily dependent economically on the Sellafield nuclear processing facility and Mr Corbyn’s past opposition to nuclear power has not gone down well. Labour sought to counter with a hard-hitting campaign focusing on possible cuts to maternity services at the West Cumberland Hospital, with a claim local midwives believed it would lead to “mothers and babies dying”.

Labour candidate Gareth Snell celebrates with his wife Sophia (PA)

Despite this, the Conservatives increased their vote share by more than eight per cent in Copeland, while Labour's was down by nearly five per cent. The Tory victory, Ms Harrison, said her victory showed, "the people are ready for change".

“I think we ran an extremely positive campaign and it was a campaign that represented the needs of this area,” she added. “And I know this area because I have lived here all of my life.”

“I think that, and the combination of Jeremy Corbyn's views on nuclear in an area which is so dependent on Sellafield and on Moorside, contributed to my win tonight,” she said.

The contests were triggered after the sitting Labour MPs Jamie Reed and Tristram Hunt – both persistent critics of the Labour leadership – quit. Mr Hunt, a former shadow Education Secretary, took up his role as the new director of the Victoria and Albert Museum in London earlier this week.

Ukip candidate and party leader Paul Nuttall at the Stoke count (PA)

Questions over Mr Nuttall’s future at the helm of Ukip are also likely to surface following his defeat in Stoke, where the party made a concerted effort to attract Labour voters. Just last week at the party’s spring conference in Bolton, former leader Nigel Farage said the by-election would be “fundamental” to the party’s future.

But Mr Nuttall struck a defiant tone after the results were announced, saying "Ukip's time will come", and adding that he planned to stand as an MP in the 2020 general election.

"I'm not going anywhere," he added.