Labour held Stoke Central but lost Copeland in byelections deemed crucial for party leaders.
The mixed result may have put back any challenge to Labour’s Jeremy Corbyn, but UKIP’s Paul Nuttall looks certain to face a backlash within his ranks.
And Theresa May was celebrating the first time a ruling party has taken a seat off the official Opposition since 1982.
Corbyn said: “Labour’s victory in Stoke is a decisive rejection of UKIP’s politics of division and dishonesty. But our message was not enough to win through in Copeland.
“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.”
But one Labour MP warned the results showed that Labour is on course for an “historic and catastrophic defeat” at the next election unless it raises its game.
Labour’s Gareth Snell held Stoke-on-Trent Central with 7,853 votes, seeing off Nuttall who got 5,233. He said voters had “chosen the politics of hope over the politics of fear”.
He added: “This city will not allow ourselves to be defined by last year’s referendum and we will not allow ourselves to be divided by the result,” adding that the result was “a victory for the whole Labour Party and Labour movement”.
However, Labour’s share of the vote was 37% – slightly down on the 39.3% it got in 2015. UKIP got 24.7% of the vote and the Conservatives, who came a close third, 24.4% – both slightly higher than their 2015 vote shares.
Nuttall said his party’s “time would come”, adding: “There’s a lot more to come from us. We are not going anywhere, I’m not going anywhere.”
UKIP chairman Paul Oakden said: “The whole narrative of Paul’s leadership depending on winning in Stoke is a nonsense.”
Labour MP Jack Dromey, who ran Snell’s campaign, said: “I think as we win we need necessary humility because there is a view that Labour is no longer listening in the way it should do. I think what we have done in this community is precisely to do that. Are we yet a credible alternative government? No we’re not. But tonight is a decisive moment.”
In Copeland, held by Labour for more than 80 years, Tory Trudy Harrison won with 13,748 votes to Gillian Troughton’s 11,601.
Mrs Harrison, who had been joined by Prime Minister Theresa May on the campaign trail, got 44.3% of the vote, increasing the Conservatives’ vote share by more than 8%. She overturned a Labour majority of more than 2,564 to take the seat by 2,147 votes – a swing of more than 6%.
Professor John Curtice, of Strathclyde University, said the Copeland result was the best by-election performance by a governing party in terms of the increase in its share of the vote since January 1966.
Mrs Harrison said: “It’s been very clear talking to people throughout this campaign that [Labour leader] Jeremy Corbyn doesn’t represent them.
“They want a party which is on the side of ordinary working people, which will respect the way we voted in the referendum and which will build a country which represents everyone. That’s why they voted for me tonight.”
John Woodcock, Labour MP for neighbouring constituency Barrow, said the defeat showed the party was “in trouble”. He said there were “always excuses” for parties after they lost by-elections and the party must be doing much better nationally.
Asked if Labour could win the next general election, he said the party was “actually on course to a historic and catastrophic defeat”. That would have “very serious consequences for all of the communities that we represent and the causes that the Labour party stands for.”
The MP said it would be “counter-productive” for him and other critics of Corbyn to demand another leadership election when the outcome was likely to be another victory for Corbyn. He added: “Jeremy Corbyn is going to remain leader of the Labour Party unless he decides that he thinks that it is right to go.”.
But Shadow Chancellor John McDonnell said Labour’s victory in the Stoke by-election showed that it was still capable of winning elections in its heartlands.
“There’s really unique circumstances in Copeland,” he added. “The Labour vote has been eroding over a number of elections now. But the issue around the future of the nuclear industry clearly dominated that election campaign. So, yes I’m really disappointed but it’s not unexpected, given the unique circumstances in Copeland itself.”