Conservative Trudy Harrison won the seat in a special election in Copeland, a rural district in the far north of England that has always been a Labour stronghold.
But some Labour legislators said the party is on a disastrous course ahead of the election in 2020.
He said: "I was elected to lead this party, I was elected to oppose austerity and to oppose the redistribution of wealth in the wrong direction, which is what this Government is doing". He said defiantly Friday that he is "proud" to lead the party and will continue to focus on the future of Britain's financially strained National Health Service as well as the issues of social care and housing. "That is the course we've taken", Corbyn told delegates.
Ms Harrison polled 13,748 votes to 11,601 for Labour's Gillian Troughton, increasing the Conservative vote share by more than 8% as Labour's dropped by almost 5%.
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In a second special election, Labour held on to its seat in Stoke-on-Trent Central, beating back a challenge by the right-wing, anti-EU U.K. Independence Party, which was represented by party leader Paul Nuttall.
"I had the support of hundreds of Labour members, MPs and Councillors from Cumbria and beyond who came and campaigned for me and they are a credit to the labour movement".
And the veteran Labour backbencher David Winnick said Mr Corbyn was an "obstacle" to victory and should consider his position.
Harrison said Corbyn did not represent "ordinary working people" in the district.
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Prosecutors said Branch AME Church also had a sign advertising a Wednesday night Bible study. Roof was sentenced to death in January after a jury convicted him of all 33 federal charges.
Corbyn loyalist Cat Smith MP defended the Labour leader, calling the party's performance in Copeland an "incredible achievement" because Labour had been "15 to 18 points behind in the polls".
Mr Corbyn was defiant when he was asked whether he should "fall on his sword" following the loss of Copeland. But our message was not enough to win through in Copeland. Both constituencies, like so many in Britain, have been let down by the political establishment.
The leader of the shopworkers' trade union Usdaw, John Hannett, said that the results "raise questions about Labour's electability and the vision it offers to the people of this country".
Lady Smith told the Huffington Post UK: " We mustn't bury our head in the sand, this is a very bad election result for us.
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