The sister of the murdered MP Jo Cox has said Labour needs more “real people” in parliament to reconnect to its former voters, as she vowed to “burst the Westminster bubble” if she wins the Batley and Spen byelection. Kim Leadbeater is aiming to follow in her late sister’s footsteps by becoming Labour MP for the West Yorkshire constituency when the contest is held in July. The campaigner and personal trainer, 45, said there was a “big disconnect between the Westminster bubble and communities like this” partly because there were too few MPs with “life experience, not just experience in politics”. “I would try and go into politics to burst the Westminster bubble and try create something a little bit different in politics by speaking for real people in the real world,” she said. The Labour leader, Keir Starmer, will be desperate to quieten his critics by retaining a seat the party has held since 1997. Labour holds Batley and Spen with a narrow majority of 3,525 and a defeat would deal a further blow to Starmer’s leadership following the Hartlepool byelection and local election losses this month. The Batley and Spen byelection was called following the resignation of Tracy Brabin, who was elected the first mayor of West Yorkshire. The contest is expected to take place in July although a firm date will be announced later this week. Speaking after being selected as Labour candidate on Sunday, Leadbeater told the Guardian the party “needs to reconnect with its roots and the fact that it is the party of working-class people”. Leadbeater said there were too few working-class MPs on the frontbenches of either major party. Asked whether Labour needed more MPs who look and sound like the voters who have left the party in recent years, she said: “I think so. I don’t think it’s impossible to be an MP for somewhere where you’re not from if you get to know the area really well and you embed yourself in that area. For me, personally, I couldn’t be an MP for anywhere else.” Leadbeater started her career in sales and went on to work in education, lecturing in physical activity, health and wellbeing at colleges in Bradford and Dewsbury. She said: “I don’t have a traditional route into politics. I actually think that’s a really positive thing and a really helpful thing. I think politics needs more real people who’ve lived a life outside politics. That’s what lots of people tell me. I think you need life experience, not just experience in politics.” Asked whether Labour had been ineffectual in opposition, given that Boris Johnson’s Conservative party enjoys a sizeable lead in the polls, she said: “Labour’s got work to do and I’m looking forward to being part of that change.” The byelection campaign will coincide with the fifth anniversary of Cox’s murder on 16 June. Leadbeater has devoted much of the past five years to continuing her sister’s legacy through the Jo Cox Foundation, which is based in Batley. Speaking while canvassing on a housing estate in Staincliffe on Tuesday, Leadbeater said standing for parliament had been “the most difficult decision I’ve ever had to make”. One of her concerns was safety, she said, given the “horrific abuse” faced by politicians in recent years. She suggested that politics had not become more civilised since Cox’s murder on the eve of the Brexit referendum, saying it remained “very adversarial, very confrontational and very aggressive”. There needed to be “more passion, more facts, but less of the nastiness,” she added. Echoing her sister’s now-famous remarks in her maiden Commons speech – that people have “far more in common than that which divides us” – Leadbeater said politicians must do more try to “bridge some of the divides” of recent years. “We need to do politics differently,” she said. “People have got every right to vote for whoever they choose but I think politicians have got a duty to uphold civility. There’s nothing wrong with disagreeing or robust debate, but we need to reduce the personal insults and the attacks and treat each other as human beings.”