Despite MPs backing proposals last year to legalise assisted dying in England and Wales, the plan did not become law. The bill failed to complete its passage through the House of Lords – not because peers voted against it, but because a relatively small number proposed an unprecedentedly large list of amendments. As a result, the bill ran out of time.

But this is unlikely to be the end of the story for assisted dying. MPs who support the change have called for the bill to be brought back in the new parliamentary session, which begins on May 13. They have reportedly been joined in their demands by almost 200 peers in the Lords.

Their strategy will be for MPs to pass the bill again in an identical form. If they do so, it could become law even if the Lords fails to pass it. This is possible because of special powers to override the Lords under what are known as the Parliament Acts. But achieving this will not be straightforward – to succeed, supporters will need to overcome four key challenges.

Challenge 1: Winning the lottery

The first challenge will be for a supporter to be drawn high in the private members’ bill ballot. At the start of each session, 20 MPs are selected from this random draw to receive priority access to the very limited Commons time available for private members’ bills. Those drawn highest pick their slots first, giving them the best chance of success.

A supporter would need to be drawn among the top seven places to guarantee a full day’s debate (and therefore a vote) on their bill – a key requirement to prevent it being “talked out”. But in reality, they probably need to be drawn in the top three. Supporters say they have around 200 MPs willing to reintroduce the bill if selected.

If advocates do not win this legislative lottery, they have other options. One is to introduce a different form of private members’ bill, known as a presentation bill, but this will struggle unless ministers grant it time. Less likely is a government bill. Either way, ministers would need to provide public assistance in ways they have so far been reluctant to.

Challenge 2: Maintaining support from MPs

The next task will be to maintain a coalition of MPs behind the bill, which would again be subject to a free vote. Although MPs backed the bill last time, supporters may be concerned that the margin of victory more than halved during its Commons passage – from 55 at the initial second reading vote to 23 at the final third reading. Fourteen MPs switched from support to opposition, while just one made the opposite journey. If this trend continued, the majority behind the bill could evaporate.

But the reverse is also possible, especially if some opponents choose to back it as a point of democratic principle. Liberal Democrat leader Ed Davey, who voted against the bill’s first iteration, has criticised as “undemocratic” the Lords’ failure to complete its scrutiny. It is possible that he and others could switch their votes.

Challenge 3: Avoiding new amendments

To be able to use the Parliament Acts to override the Lords, MPs would need to back the new bill in essentially an identical form to the first time. During the first bill’s passage, MPs made more than 200 amendments. Supporters will want to avoid doing so again.

MPs can amend bills at their committee and report stages. On the few occasions when the Parliament Acts have been used, ministers have usually moved a motion to effectively cancel these stages – preventing MPs from making changes. But the Parliament Acts have never before been used on a private members’ bill, and it is unclear how these stages could be avoided without government assistance.

Otherwise, these stages would proceed as normal. This would not only slow the bill’s passage through the Commons but would also risk the bill being amended – which would of course prevent the Parliament Acts being used. As such, any amendment passed in the Commons could effectively scupper the bill. This could provide cover for opponents who would prefer not to be seen blocking the bill outright.

Challenge 4: Incorporating amendments they do want

There is another snag for supporters of the assisted dying bill. The version of the bill passed last year by MPs is not the version they would ideally like to see on the statute book. Supporters cannot include any changes when they ask MPs to vote again for bill, but they will want to add some later.

For instance, Labour peer Charlie Falconer, the bill’s sponsor in the Lords, proposed almost 80 amendments last time – typically implementing changes requested by government lawyers, or responding to parliamentary pressure including from influential Lords committees. The slow pace of Lords scrutiny meant that most of these were never reached.

The Parliament Acts provide a mechanism to deal with this: an unusual “suggested amendments” process, enabling MPs to send the amendments to the Lords alongside an otherwise-identical bill. But this process would probably require ministers to provide Commons time.

Over to the Lords (part two)

Making it around these obstacles would require a combination of luck, tactical nous and sustained popular support. It is also likely that it will require a more overt helping hand from ministers on the process – though the government will remain neutral on the policy. Such assistance seems more doubtful if Prime Minister Keir Starmer is ousted.

If the bill makes it to the Lords a second time, and in an identical form, it would then be up to peers to scrutinise it again. But whereas last time opponents in the Lords had incentives to drag out scrutiny, this time their best interests would be served by reaching agreement on safeguards before the session ends. Because, if they fail to do so, the bill could be passed into law regardless.

Yet just because MPs could override the Lords, it does not mean they necessarily will: some form of compromise seems more likely. If peers amend the bill a second time around, MPs could still accept these changes. And we shouldn’t forget that, given the breadth of expertise in the Lords, doing so could also make for a better law.