Christian campaigners are appealing to MPs to reject proposals to legalise assisted suicide.
Many of them will be gathered outside Parliament this morning as MPs debate Kim Leadbeater's Terminally Ill Adults (End of Life) Bill, which would allow assisted suicide for some terminally ill adults who have been given less than six months to live.
Andrea Williams, chief executive of Christian Concern, which has been running a campaign against the bill, said: “This vote is the most profound threat to life in our nation since 1967.
"Now is the time for us all to resist assisted suicide."
She added, "Right now, everyone has a chance to help prevent the United Kingdom from choosing death. If we cross this line, it could take decades to reverse the damage.”
The vote is reported to be on a knife-edge after a number of MPs who had initially given their backing turned against it in the last few days. They include four Labour MPs who made a last-minute switch over the removal of a key safeguard - replacing approval by a High Court judge with a panel.
Shadow Justice Secretary Robert Jenrick and Christian MP Tim Farron are among those who have said they will be voting against the bill.
The Royal College of Psychiatrists (RCPsych), the Royal College of Pathologists and the Royal College of Physicians have all raised concerns about it.
Christian Concern has been leading the No Way Back campaign against the bill in the days leading up to today's vote, which will see the bill passed on to the House of Lords for further revision or rejected altogether.
The campaign includes a video warning about the harms of assisted suicide and a website with more information and resources, including a tool to contact MPs.
At the centre of the campaign is the message that assisted suicide is dangerous, especially for disabled and terminally ill individuals.
Paul Huxley, a spokesman for the No Way Back campaign, said: "The availability of assisted suicide puts additional burden on terminally ill people to decide whether their lives are worth living.
"Even where there is no explicit coercion, people are very easily made to feel that others would be better off without them.
"This is even more of a risk with this bill's poor safeguards. Doctors will be allowed to raise assisted suicide with patients, increasing the perceived pressure on them to take their lives."
He pointed to the example of Oregon in the US, where nearly half of patients who chose assisted suicide (43%) cited 'feeling like a burden' as a factor in their decision.
He expects that whatever safeguards are initially put in place in the UK will be gradually eroded, as has happened in other countries where it is already legal.
"Similar or worse figures are seen in Washington State, Canada and other jurisdictions that provide assisted suicide or euthanasia," he continued.
"Assisted suicide is never compassionate. It leaves vulnerable people in the position of justifying their continued treatment and existence.
"What's more, once this line has been crossed, safeguards and restrictions are consistently relaxed. In Canada, for example, there are multiple instances of individuals undergoing euthanasia or being prompted to consider suicide due to poverty, housing issues, and mental health conditions.
"Terminally ill people deserve better care, not suicide."
Alithea Williams, public policy manager at the Society for the Protection of Unborn Children, said Friday's vote was "crucial".
"If it goes to the House of Lords, Peers can amend it, but MPs will only vote again on their amendments, not on the bill as a whole," she said.
Gordon Macdonald, CEO of Care Not Killing, handed in a petition to 10 Downing Street this week signed by thousands of people opposing the plans.
"Any MP who still has concerns about this bill cannot hope that peers will fix what the Commons did not — they must vote no," he said.
On the eve of the vote, fresh polling by Care Not Killing found that over a third of Brits are unclear about what assisted dying actually means.
According to the poll of over 2,000 UK adults, over a fifth (22 per cent) think it means “giving people who are dying the right to stop life-prolonging treatment”, while around one in 10 (9 per cent) think it means giving “deep sedation to relieve suffering in the last days or hours of life, sometimes leading to unconsciousness until death”.
A further 3 per cent think it means “providing hospice-type care to people who are dying” and 2 per cent believe it to be "a medical directive that no attempts should be made to restart the heart or breathing if they stop".
A separate poll by Whitestone Insight for the disability rights group Not Dead Yet UK found that a significant majority of the British public (63%) are concerned that the proposals could lead to disabled people feeling pressured to end their lives. This rose to over two-thirds (67%) among respondents living with a disability.
Three in five of all respondents feared that some disabled people could be coerced into assisted suicide by others who do not have their best interests at heart, rising to 64% among disabled respondents.
