Labour backbench MP Kim Leadbeater has introduced a bill in the House of Commons that aims to legalise assisted dying in England and Wales.

Leadbeater is not a member of the government, but has been able to introduce the terminally ill adults (end of life) bill after topping this session’s private members’ bill ballot in September.

It’s almost a decade since MPs last voted on assisted dying. Back then, the Conservatives had a majority. Now, the tables have turned and Labour has a large majority. However, it’s not yet clear whether the current cohort of MPs would back this momentous change.

Leadbeater’s bill faces additional procedural challenges. Private members’ bills – legislation sponsored by individual MPs rather than the government – face a precarious route onto the statute book. They are highly vulnerable to objections, even if only from a small number of MPs.

While private members’ bills go through the same basic process to become law as government-sponsored legislation, they are awarded only limited parliamentary time. There are only 13 Fridays per session (typically a year) when these bills are discussed in the House of Commons.

Challenge 1: second reading

The first major test for this bill will be its second reading stage, due on November 29. For backbench bills, and especially those that are contentious, this stage can be tricky.

Private members’ bills aren’t “programmed” like government bills, which means there is no mechanism for allocating more time to their discussion if needed. So, it only takes a small numbers of MPs to frustrate a bill’s progress by talking at length to run down the clock.

To prevent this, supporters can attempt to move the “closure” – a motion to end the debate and make a decision. This, however, requires at least 100 MPs to vote in support – a difficult feat on Fridays, when most MPs are in their constituencies. This problem was illustrated earlier this year on a bill to outlaw conversion therapy. However, on a bill of this profile, there is a good chance of passing the closure.

For Leadbeater’s bill, simply getting a vote at this stage would be an important accomplishment. It would mean that for the first time since 2015 – also on a backbench bill – the opinion of the Commons could be tested on assisted dying.

Challenge 2: public evidence?

Assuming the assisted dying bill passes the second reading stage, it would then be sent to a public bill committee for detailed consideration.

Unlike for government bills, this committee cannot, by default, hold public evidence sessions on backbench bills. For a reform of this significance, though, we should expect pressure from some MPs for an exception to be made to allow outside bodies – such as campaign groups, religious organisations and medical professionals – to submit evidence. This would delay the bill’s passage a little, though this need not be lengthy.

Challenge 3: report stage

The bill’s biggest test is likely to be at report stage – most likely on April 25 next year. This is when the bill returns to the House of Commons chamber.

Conventional wisdom is that this stage is often fatal for contentious backbench bills, since opponents can propose large numbers of amendments to the legislation, requiring many separate decisions to be made and time to be drained. Even if supporters attempt to move the closure, with enough amendments they may still run out of time. Something like this nearly happened on an EU referendum bill in 2013.

Yet, this conventional wisdom may be outdated. The speaker of the house routinely groups report-stage amendments together, reducing the number of separate decisions – and in recent years the norm has been a single group. Since 2019, there has never been more than one group of amendments up for consideration on any private member’s bill. If the speaker follows this recent practice, it may be easier to get the bill through report stage.

Challenge 4: out of time?

It is quite possible the assisted dying bill could overcome all these procedural hurdles. But if not, ministers may need to step in to set aside some of the government’s own parliamentary time to discuss the bill further.

Government time for backbench bills has been rare in recent years, although it did occur in 2019 during the passage of a bill to strengthen the laws around female genital mutilation. But there are some striking historical precedents.

In the 1960s, private members’ bills were used to pass major social reforms on the laws around homosexuality and abortion, and to abolish the death penalty. In all three cases, the government stepped in to dedicate extra time in the face of attempts to slow these bills’ progress.

Challenge 5: up to the Lords

If the bill makes it past these stages, then it also has a good chance of completing its final House of Commons (third reading) stage. But it would then need to complete a similar process in the House of Lords. While there are not quite the same time pressures in this chamber – notably, it does not have the same system of 13 Fridays – there is also no programming for any bills.

It is hard to predict exactly how the Lords would respond to an assisted dying bill. There have been multiple previous attempts to legislate on this matter over the years. The last time one reached committee stage, in 2015, it got bogged down with amendments and made it no further.

Leadbeater’s bill will be helped by another bill on assisted dying, started in the House of Lords by Labour peer Charlie Falconer. This is scheduled for debate in the coming months and may help identify and resolve some of the detailed points of contention – though this is not guaranteed.

It would be unusual, though not impossible, for the Lords to fail to pass a private member’s bill agreed by the House of Commons. Since 2010, there appear to have been only two that were actively held up in the Lords – as opposed to just running out of time. Even so, a small number of determined opponents to assisted dying could make life difficult.

Were this to happen – at this point an extreme hypothetical – one option available to MPs would be to re-introduce the bill in the subsequent session, perhaps from the new crop of ballot bills. Under the provisions of the Parliament Act(s), this bill might then be eligible to become law without the assent of the Lords. Such a situation very nearly occurred this year on another backbench bill, on hunting trophies, though the timing of the general election intervened.

Despite these procedural hurdles, the assisted dying bill has a reasonably good chance of passing into law. In the end, much will depend on whether MPs are willing to back this change, and how determined they are to do so.