The archbishop of Canterbury has warned that legalising assisted dying is dangerous and risks turning the right to die into a duty.
His intervention came before the formal introduction of a private members’ bill in the Commons on Wednesday that aims to offer choice at the end of life.
Speaking BBC Newsnight, Justin Welby said: “I think this approach is both dangerous and sets us in a direction which is even more dangerous, and in every other place where it’s been done, has led to a slippery slope.”
And writing in the Daily Mail he said: “The right to end your life could all too easily – all too accidentally – turn into a duty to do so.”
He added: “I worry that even the best intentions can lead to unintended consequences, and that the desire to help our neighbour could, unintentionally, open the door to yet more pain and suffering for those we are trying to help.”
The bill is being brought forward by the Labour MP Kim Leadbeater, who has said that any change in the law would be “potentially one of the most important changes in legislation that we will ever see in this country”.
Asked about Welby’s concern that the introduction of a limited right to assisted death has led to more far-reaching changes in other parts of the world, she said: “That’s not true.”
She cited the US state of Oregon, where the right of those who are terminally ill to have an assisted death has not been broadened since it was introduced in 1997.
Related: Vulnerable people not at risk from proposed assisted dying law, says MP
Leadbeater said: “I have got huge amounts of respect for the archbishop of Canterbury, but that isn’t true. There are places where this has been an option for people at the end of life. I think Oregon is the one where for 25 years the law has not broadened out, it has stayed.”
She told the BBC: “There has to be a change in the law, I’m very clear about that, but we’ve got to get the detail right.
“This is about terminally ill people. This is not about people with disabilities, it’s not about people with mental health conditions, it’s very much about terminally ill people.”
She told the programme that she would like to see a “timeframe” on the diagnosis of patients, and said she had been having meetings with medical organisations including hospices because she was “very keen to make sure that the medical professionals are involved in this conversation”.
It was put to Leadbeater on the programme that she would want the bill to require two medical professionals and a judge to agree, to which the MP said: “Yeah, I think there needs to be medical safeguarding and also judicial safeguarding.
“And as many layers of that as possible to make sure that people are given this really important choice that I firmly believe people deserve when they are at the end of their life, but to make sure that it’s a robust process to get to that point.”
High-profile supporters of legalising assisted dying include Dame Esther Rantzen who is terminally ill and has pleaded with the public to write to their MPs to ask for “the right to choose, not to shorten our lives, but to shorten our deaths”.
The wording of the bill has not yet been published but some of those in favour have urged that it includes people facing unbearable suffering as well as those who are terminally ill.
MPs will have a free vote in parliament, deciding according to their conscience rather than along party lines. The prime minister, Keir Starmer, has previously supported assisted dying and made a personal promise to Rantzen to make time for a debate and vote on the issue.
Starmer has previously said he was “personally in favour of changing the law” and supported a change the last time the issue was voted on in the Commons nine years ago.
Last week, he called the matter a “really important issue” and said any change to the law must be “effective” but he has insisted the government will remain neutral in a vote.