When Kim Leadbeater came top of the ballot of private members’ bills, she did not immediately decide to attempt a generational change in the way the British state handles life and death. But, she says, it was an opportunity that rarely comes for a backbench MP. The past few months campaigning for her bill to legalise assisted dying have exhausted her. It has been a licence for everyone she meets – in parliament, in the street, everywhere in her life – to tell harrowing stories. “I’m emotionally ruined,” she said in her Commons office, among piles of folders containing photos of people who have told her stories about their suffering. “I literally cannot walk down the street without someone stopping me and telling me the story about someone who’s died.” Her decision to bring the bill has meant a record number of new MPs will on Friday be faced with a conscience issue that could define this parliament. Terminally ill people and their families will gather outside parliament to make their final pleas to MPs to vote this through. Disability activists who are against the changes will also be there to hold a rally. It would be an emotional moment for even the hardest Commons veteran. But because of the sheer numbers, it will be the new intake who are the deciding voice. The debate has become increasingly bitter, especially after calls from the health secretary, Wes Streeting, to vote down the bill on the grounds of the state of the NHS, an intervention that infuriated one side but struck a chord with many of those who were conflicted. MPs on either side have made unlikely alliances – Conservative cabinet veterans alongside new Labour MPs who have deposed their Tory colleagues. Evangelical Christians have found themselves organising in their offices alongside atheist trade unionists. Leadbeater heard from a number of other causes that lobbied for her attention in the fortnight it took for her to reach her decision on the bill. It would be wrong to say Leadbeater was not influenced by Keir Starmer’s decision to promise Esther Rantzen that a vote would be held, but Leadbeater says she was motivated primarily by the personal stories she heard. There was no approach from Starmer personally. But when Leadbeater decided she would take up the cause, there was a private approach to Downing Street to see if there were objections – and there were none. Starmer has been studiously neutral in the lead-up to the vote, but privately he has been appalled by the public comments of his cabinet ministers – particularly Streeting, whom he has told to stop his interventions. The prime minister’s own view was formed during his time as director of public prosecutions: that the current law is not fit for purpose and puts families at risk of arrest and where patients take their own lives in ways that are dangerous and painful. He will vote on Friday, though he has not confirmed which way, and there is a strong feeling among the bill’s proponents that it will be a decisive moment. “When you watch the prime minister walk through the yes lobby, lots will think: ‘that’s good enough for me,’” said one MP. When Leadbeater first adopted the bill, there were raised eyebrows. She had never spoken on the issue previously, though her sister Jo Cox, the former MP who was murdered by a far-right terrorist, had been a strong advocate. But the prime minister is an outlier in his own operation. “There was no No 10 machine behind this,” said one ally. “The machine is not actually sure they want this to happen.” Senior aides are frustrated the cause is dominating the conversation and the divisions it is causing. “It’s a nightmare,” one official said. “If it passes, it will eat up so much time. And it’s causing divisions among our MPs when we have worked so hard to try to build bonds between them.” “Keir wanted it to happen,” another staffer said. “It’s that simple. There isn’t anyone else who thought this was a particularly great thing to do in the first months of a Labour government.” Proponents of the change have been privately irritated at the prime minister’s lack of public support for the cause. But it was Starmer who instructed Simon Case, the cabinet secretary, to write to cabinet ministers telling them to keep out of the debate. However, Starmer’s silence has left the forum open for Streeting and the justice secretary, Shabana Mahmood, to make all the headlines with their opposition. Streeting said he feared for the state of the NHS and palliative care, saying it was not fit to provide the safeguards. His comments came in a private meeting of Labour MPs – but it was obvious they would leak. It is a fear some in Downing Street broadly share, however. “The NHS is our absolute first priority in government, it’s what we will be judged on, how have we got ourselves in the situation where the first thing we are seen to be offering is making it easier for people to die?” one government official said. There are some in No 10, however, who think there will be a positive political impact. “You can’t deny it is something that is very popular with the wider public, and if it does pass it will be a totemic thing to have done,” one Starmer aide said. Should the bill pass on Friday, the work would already have begun. “Government will spring into action,” said one official. “We cannot have a situation like the Brexit vote where no preparatory work was allowed.” Streeting has told colleagues he will move to “make-it-work mode” – likely to head off any rumours that he would resign. At the next stage, if the bill passes to committee, a government minister will be assigned to it, likely to be the Ministry of Justice’s Heidi Alexander. Stephen Kinnock, the care minister, will lead the work in the Department of Health and Social Care. Leadbeater has promised that there will be spaces on the bill committee in parliament for opponents who are willing to work constructively. But there are also very likely to be a number of government amendments at the next stage – including lengthening the amount of time until the bill must be implemented after royal assent, defined in the current bill as two years. There is already tentative talk about how to gain a broader consensus on the issue whether the bill passes or not – perhaps with a royal or parliamentary commission. More than 160 MPs have put their names down to speak at the five-hour debate. Dozens of those who will be listening have said they may wait until then to make a decision. MPs who had no prior firm view on the topic have distressing case studies from constituents – on both sides – landing in their inboxes. One described having been lobbied by a local bishop. There have been tearful community meetings in village halls and libraries. It has been, for many, overwhelming and dozens are still undecided. The pro-assisted dying campaign had a solid parliamentary operation from early in the parliament. Labour MPs divided up their parliamentary intakes and appointed “whips” for each different generation of MPs to go through the numbers. The group meets three times a week in Leadbeater’s office and are now quietly confident that if all the pledges of support carry through, the bill will pass. “Kim has been saying to MPs, this might be the most important decision you ever make in your parliamentary careers,” one MP said. Among those working on the campaign are two Conservative ex-cabinet ministers, Kit Malthouse and Andrew Mitchell. Working their intake are some of the most talked-up talents in the new cohort of Labour MPs, including Josh Simons, Jeevun Sandher and Lloyd Hatton. A doctor in parliament who is in favour, Peter Prinsley, said he found it easier to convince older colleagues. “They are more likely to have encountered those who have had a difficult death,” he said. “But this new cohort of Labour MPs is very young, it can feel more distant for them, so that has been a challenge.” For those opposed, the organisation remains more splintered. Labour MPs who are against the change know many of their colleagues will not be convinced by religious Christian arguments such as those from the Conservative MP Danny Kruger or Labour’s Rachael Maskell. The involvement of groups such as Right to Life, who also oppose abortion, has made the association very tricky for atheist MPs. Despite a less centralised operation, it is this group who have had the most high-profile interventions, including Streeting and Mahmood, the former prime minister Gordon Brown and the mother and father of the House, Diane Abbott and Edward Leigh. The most visible campaigners against the change in politics have been disabled parliamentarians such as Baroness Tanni Grey-Thompson or the MSP Pam Duncan-Glancy. The debate has taken its toll on many of them, saying they believe disabled people’s voices are being crowded out. Many have experiences with intolerable waits for assistance and funding for care – the idea the state will make it quicker to request an assisted death than to get a ramp at home is one example that gives MPs pause. The MP Antonia Bance, who was previously a senior official in the TUC, and James Frith, the Bury North MP who regained his seat from the Tories in July, have been making the equality case to colleagues. “I oppose this bill precisely because my values are Labour, trade unionist and collectivist,” Bance said. “I know that sometimes the collective good – in particular protecting vulnerable people and those with protected characteristics, such as disabled people and women – means that we must impose limits on individuals’ freedoms.” In the final hours before the vote, its advocates will make the case to MPs who have doubts that they should take the bill to the next stage and make the case for changes. But it will also means that, even if the bill passes, its opponents will hope there is still time to change parliament’s mind.