The sister of the murdered MP Jo Cox is considering standing for Labour in the Batley and Spen 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, has told friends she is considering running as the Labour candidate in what would be her first entry into politics. Leadbeater, 44, is a campaigner who lives locally and is an ambassador for the Jo Cox Foundation, which is dedicated to continuing her sister’s legacy. 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. The Labour leader, Keir Starmer, is under huge pressure over the party’s performance in its former heartlands following a devastating defeat in the Hartlepool byelection. Losing another seat to the Conservatives would embolden his critics. Leadbeater, leader of the More in Common Batley and Spen community volunteer group, was awarded an MBE in the new year honours in December for her work tackling social isolation during the Covid-19 pandemic. She is the most high-profile name to emerge so far as a potential candidate. One local Labour source said some unions were waiting to see whether Leadbeater stood before deciding which candidate to back. Another Labour figure said Leadbeater would “cut through” any attempt by rival parties to inflame a row over the suspension of the Batley grammar school teacher who showed a cartoon of the prophet Muhammad, prompting days of protests in the constituency in March. Paula Sherriff, the former Labour MP for neighbouring Dewsbury, is also considering putting her name forward. She is understood to want to return to Westminster after losing her seat in 2019. Labour’s candidate is expected to be shortlisted in the coming weeks and chosen by a vote of local members, a reversion to the standard procedure after an outcry by some members after Paul Williams was selected to run in Hartlepool without a vote, due to the snap byelection. A date for the byelection has not yet been set but it is understood 22 July has been suggested. There is some discussion about holding the contest in mid-June, the earliest opportunity. However, this would clash with the fifth anniversary of Cox’s murder, on 16 June. Lisa Johnson, the GMB union’s external relations director, who is seen as a key Labour power player, had been tipped for the candidacy but said she was not interested. Salma Arif, a Leeds council cabinet member, has been mooted, as has Habiban Zaman, a Batley East councillor. Dan Howard, a Labour party press officer who worked for Cox’s predecessor, has also put his name forward.