Fewer than 1,000 patients a year in England and Wales are expected to choose assisted dying should the law pass, the Labour MP Kim Leadbeater said, as she outlined her bill setting out the change.

But MPs opposed to the measure said they were deeply concerned by several components, including that the proposed legislation did not bar doctors from suggesting assisted dying as an option to patients.

MPs who spoke on the panel expressed significant doubts about whether the legislation would pass the first parliamentary stage in the Commons on 29 November. Leadbeater said she would make the case “literally every day” but that there were strong views on all sides.

“This is potentially one of the biggest things we will do as members of parliament in our careers,” Leadbeater said.

The Conservative MP Kit Malthouse, who backs the bill, said he thought a significant number of MPs who had voted against the measure in 2015 had changed their minds.

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But Dr Peter Prinsley, a Labour MP who is also a consultant, said he believed some of the new, younger MPs were wavering. “I’m not as confident of this thing passing as I was before I started having these conversations,” he said.

“If you’re maybe a bit younger and you haven’t encountered people who die in horrible circumstances, or take their own lives or whatever, maybe you’re a little bit removed from it. Anybody I speak to who has experienced things as they are now cannot understand why we’ve not made this change.”

Prinsley said he feared many MPs would abstain and urged them to vote – whatever they decided. “I don’t think that abstaining, which people may be tempted to do, is a neutral act. I think that people need to make a decision about this, and that’s what I’m encouraging people to do,” he said.

The assisted dying bill: what it means for patients in England and Wales

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Setting out the safeguards in the bill, Leadbeater and the Labour peer Charlie Falconer said there was no legal risk of its scope being widened by the courts on human rights grounds, because of the strictly limited definitions in the bill and the failure of previous challenges in British and European courts.

Leadbeater said the numbers of those taking up the option would be low because of the strict criteria: assisted dying would be offered only to patients with a terminal diagnosis with a prognosis of less than six months. It would not be available to people with longer to live who may be suffering, such as those in the earlier stages of motor neurone disease.

The procedure has to be self-administered, Leadbeater said – in jurisdictions where doctors are allowed to help patients take their own lives, the numbers are higher.

Leadbeater defended the fact that the bill did not prohibit doctors from discussing assisted dying with patients – which has caused controversy in jurisdictions such as Canada. Doctors will not be obliged to speak to patients about it, the bill says, but must use their judgment.

The MP said the British Medical Association thought it was necessary that doctors could “discuss the range of options that are available to patients”.

But Dr David Nicholls, a consultant on the panel, said he would be disinclined to do so. “That’s not something I would necessarily [do],” he said. “The risk is, you don’t know what that patient thinks.”

The bill, which would legalise assisted dying in England and Wales, has safeguards including lengthy prison sentences for coercion and powers for judges to cross-examine patients.

Two doctors and a high court judge must sign off any decision, which Leadbeater said would mean a full hearing with evidence from the patient and doctors – although in practice the judge would check only that the terms of the act had been met, rather than examining motivation.

Lord Falconer, the former attorney general who is supporting the bill, said he disagreed that the act could be challenged in court and expanded. He said it was possible for a case to be brought by disabled adults who could say the bill was discriminatory, but he believed any such challenge would have no prospect of success.

“The English courts and the European court of human rights in Strasbourg have said time and time and time again, assisted dying is not something prescribed by the convention,” he said.

“It is for legislatures to decide … they recognise there are spiritual, there are religious, there are ethical approaches that differ from one country to another. Any such application would be hopeless,” he said.