The sister of the murdered MP Jo Cox has said she would be “honoured” to represent the people of Batley and Spen as she announced her intention to become Labour’s candidate in the upcoming byelection. Labour is facing a huge test to cling on to the West Yorkshire constituency where Cox was killed by a far-right terrorist in June 2016. Her sister, Kim Leadbeater, confirmed on Wednesday that she hoped to become Labour’s candidate, a day after the Guardian revealed that she was considering the move. Leadbeater, 44, said she had never seen herself as a “political animal” but added: “I care deeply about the area where I was born and have always lived, and where the people are second to none. “Through all the work I have done with Jo’s foundation over the past five years I have met so many truly fantastic people from across this area, some of them Labour, many not involved in party politics at all. “This community picked me up when I needed it most and I will be forever grateful.” Labour is defending a slender majority of 3,525 votes in a seat it has held since 1997. The byelection was called after Tracy Brabin, the local MP, was elected as the first mayor of West Yorkshire on Sunday. Keir Starmer is under huge pressure over the party’s performance in its former heartlands after a devastating defeat in the Hartlepool byelection last week. Losing another seat to the Conservatives would embolden the Labour leader’s critics. Leadbeater is the most high-profile name to emerge so far as a potential candidate and she is expected to be a popular choice among local Labour members, who will choose their candidate from a shortlist in the coming weeks. In a statement, Leadbeater said the prospect of the byelection had “affected me deeply in ways I really hadn’t expected”. On 16 June it will be five years since Cox was murdered, making that a potentially significant date in the campaign. A date for the byelection has not yet been set but it is understood 22 July has been suggested. Leadbeater said she had learned how “disillusioned and disengaged” people were with politics and how worried they were about the future of their towns and villages. She added: “I would love to represent this extraordinary, vibrant place that I have called home all my life. I am touched that so many people seem to think I would do a good job and I can promise that if they want me I will give my all for Batley and Spen at Westminster.”