Jeremy Corbyn said the politics of hope helped defeat the Brexit Party in the Peterborough by-election, adding that Labour is ready for a general election and should be written off “at your peril”.
Labour candidate Lisa Forbes secured a narrow majority of 683 votes over Nigel Farage’s new party, as the Conservatives fell back into third place.
The constituency, which voted 60.9% for Leave in the 2016 referendum, had been regarded as potentially fertile ground for the Brexit Party.
Mr Corbyn, addressing a crowd of journalists in the city centre as a passer-by heckled, said: “What we did was offer the politics of hope, not the politics of fear.
“We offered the politics of hope to end austerity, to fund our schools properly, to employ our police properly, to give our young people a future in this country.
“Everybody, all the experts wrote Lisa off. All the experts wrote Labour off yesterday. Write Labour off at your peril.
“We are strong, we are very determined to offer that politics that invests in decent services, in decent housing, in decent healthcare and in good quality jobs for the future and a relationship with Europe that doesn’t take us over a cliff edge but protects jobs, protects investment and gives our young people a future.”
He added: “On the day that Theresa May ceases to be leader of the Conservative Party my message is to all the squabbling contenders for the Tory party leadership, bring it on.
“We are ready for a general election.”
He said Ms Forbes would be a “wonderful MP”.
Ms Forbes said the “hard work starts now”, adding that she wants to address issues in education as well as fly-tipping and littering.
The by-election was called after Peterborough’s previous MP Fiona Onasanya was forced out after she was jailed for lying about a speeding offence.
Onasanya was elected as a Labour MP in 2017 with a wafer-thin majority of 607 but was suspended from the party after she was sentenced.