MPs are debating whether to allow terminally ill adults to end their own lives, ahead of a crucial vote in the House of Commons.

The vote will take place at about 2pm and if MPs back the bill, proposed by Labour’s Kim Leadbeater, it will go to the House of Lords for further scrutiny.

When the Commons first voted on the bill last year, it passed with a majority of 55 – since then at least a dozen MPs have switched to opposing the bill, but Leadbeater has said she is confident it will pass.

Opening the debate in Parliament, Leadbeater told MPs: “Either we vote for the safe effective workable reform contained in this bill or we say the status quo is acceptable.”

She recounted stories from terminally ill people and their families including a man called Warwick whose wife Ann “begged him to put an end to her suffering – but he didn’t want the last memory she had of him to be stood over her with a pillow”.

The last time MPs debated a bill to introduce assisted dying was in 2015 and Leadbeater said it “fills me with despair to think MPs could be here in another 10 years time hearing the same stories”.

She added: “If we don’t vote to change the law today what does that mean? It means we will have many more years of heart-breaking stories from terminally ill people and their families, of pain and trauma, suicide attempts, PTSD, lonely trips to Switzerland, police investigations and everything else we have all heard over recent months.”

Speaking against the bill, Conservative MP James Cleverly said he was struck by the number of medical professional bodies who were neutral on the principle of assisted dying but were opposed to the specific measures in the bill.

“When the people upon whom we rely to deliver this say we are not ready… we should listen,” he said.

He also disagreed with Leadbeater that it was a “now or never moment” arguing that there would be “plenty of opportunities” to return to the subject in the future.

Labour’s Diane Abbott – the longest serving female MP in the House of Commons – said there was “no doubt that if this bill is passed in its current form, people will lose their lives who do not need to, and they will be amongst the most vulnerable and marginalised in our society”.

Another Labour MP Peter Prinsley recounted his experience as a doctor and said he believed the bill would give terminally ill people “final peace of mind”.

“There is an absolute sanctity of human life, but we are not dealing with life or death – we are dealing with death or death.

“For there is also a sanctity of human dignity and fundamental to that is surely choice – who we to deny that to the dying?”

At the start of the day, MPs voted on a series of amendments that had been debated last week.

These included a measure to close the so-called “anorexia loophole” which would stop people qualifying for assisted dying on the basis of life-threatening malnutrition.

MPs backed that amendment as well as one requiring the government to publish a review of palliative care services within a year of the bill passing.

Attempts to block access to assisted dying for people suffering mental health problems or because they feel “burdensome” was defeated by a majority of 53.