New Kingswood MP Damien Egan said 14 years of Conservative government have “sucked the hope out of our country”.
The former mayor of Lewisham in London, who resigned to fight the by-election, overturned a Conservative majority of 11,220, securing 11,176 votes and a majority of 2,501.
He said: “In Kingswood, as across the country, 14 years of Conservative government have sucked the hope out of our country with a feeling that no matter how hard you work, you just can’t move forward.
“And with Rishi (Sunak)’s recession we’re left again paying more and getting less. It doesn’t have to be this way, you know it, I know it, we all know it.
“When the Prime Minister finally finds the courage to give the people a say, we’re going to need each and every one of you again to come out and vote and make sure your voices are heard.
“Our country is at a crossroads. Under the Conservatives we can choose more managed decline, more chaos, more division or we can choose a changed Labour Party.
“A government that will put people first, ensures the child’s background isn’t a barrier to their future and that will rebuild Great Britain.”
Speaking afterwards, he said: “It really hasn’t really sunk in yet. We talked to people about the issues they cared about – the cost-of-living crisis, policing and the NHS.”
Speaking from the election count, Conservative North East Somerset MP Sir Jacob Rees-Mogg said: “Does it tell you anything about the general election? Almost certainly not.
“By-elections are an opportunity for people not to turn out, to protest, and at ensuing general elections they don’t give a consistent guide to what happens.”
He added: “I think we should learn from this result and look at what happened with the Reform Party vote. Conservative Party votes are most likely to come from people who stay at home or who voted Reform.
“How do we win them back to the Tory family? People who share many views and values with us. By delivering things they believe in and that means lower taxation, taking more of the advantages of Brexit, with more of the removal of EU retained law, it means doing less on the green issue that is making people cold and poor, and helping revitalise our economy.”
But Sir Jacob said the Conservative Party did not need to change direction.
“I don’t think it would be right to do any sort of U-turns. I think we leave those to the Labour Party who are getting quite good at them at the moment.
“I think the challenge here is to focus on the policies that are Conservative and that Conservatives have always attached importance to and that appeal to those people who voted Reform at this by-election.
“I wouldn’t expect any deals, I think you have to win people over by argument and persuasion. Nobody has a divine right to anybody’s vote and you have to win it.
“They will vote Conservative if the Conservatives are saying things that appeal to them.”
Also speaking from the Kingswood count, veteran Labour MP Sir Chris Bryant said: “This result here is in the top 10 for Labour.
“You can’t immediately abstract from one seat to another, but for Jacob Rees-Mogg this is a bit of problem because 50% of this seat goes into his seat.
“If I were him, I wouldn’t be happy. They also ran a very nasty, negative campaign. We ran a campaign based on Damien’s plan and what he wanted to get done for Kingswood and what he wanted to campaign for.”