MPs opposed to no deal need to take control of Order Paper - SO24 is one way they can do it.
Not wanting to give the game away ahead of Tuesday’s showdown in parliament, opposition and rebel Conservative MPs have been coy about how they are going to prevent Boris Johnson from taking the UK out of the European Union without a deal on October 31.
But one thing is clear: if opponents of a no deal Brexit want to force Johnson's hand, they will need to get control of the parliamentary Order Paper, the daily schedule of the House of Commons. Johnson is unlikely to simply give parliamentary time to his critics, so they have little choice but to take it.
Central to the strategy will be Standing Order 24 (SO24), under which an MP can ask the speaker of the House of Commons for an Emergency Debate. The MP then has three minutes to justify why that debate is needed, and the speaker decides whether to allow it.
Given that the current speaker, John Bercow, recently branded Johnson’s decision to suspend parliament “a constitutional outrage’, it is likely that he will approve the motion.
Then what happens?
This is untested ground, Maddy Thimont Jack, senior researcher at the Institute for Government, told Euronews.
SO24s are typically used to trigger a debate on a subject that was not on the parliamentary schedule but what MPs will likely try and do Tuesday goes far beyond that,
“Normally [an emergency debate] is an opportunity for MPs to have a debate on something. What MPs are going to try to do is table a substantive motion. To use an emergency debate in this way is completely unprecedented,” she said.
Given that, the government will likely raise points of order to resist the debate, but providing the speaker allows it and MPs approve it, there is little the government can do to stop it.
And then what happens?
When the debate is held - either later on Tuesday or at some point on Wednesday - another MP will then introduce legislation to compel Johnson to extend Article 50, effectively ruling out a no deal Brexit. MPs will vote.
Given that Johnson’s majority in the Commons is just one MP, it may well pass.
“Essentially if MPs have the numbers they should be able to get it through the Commons,” said Daniel Gover at the Queen Mary University of London.
After the Commons, the law will go to the House of Lords - which is where things get more complicated.
Unlike in the Commons - where there is a three hour limit on emergency debates - in the Lords there is no such limit. Lords close to the government could theoretically filibuster - essentially waste time - the bill until parliament is suspended on or soon after September 9.
If the bill doesn’t pass before parliament is prorogued, it is effectively dead. If Johnson’s critics wanted to re-introduce it after October 14 - when parliament returns - they would have to go through the whole process again.
But what about an election?
For Johnson, an election could be a win-win. Not only will it mean the suspension of parliament during the campaign, but it will allow him to run as the Brexit candidate against an opposition that are united against no deal but not a lot else.
But experts point out that since 2010, the British prime minister is not able to call an election - he or she can only ask MPs to vote for one. Most would agree (Corbyn is certainly up for it), but could the opposition make it conditional on the extension of Article 50?
“MPs would be likely to ask for assurances that the UK will not leave the EU without a deal during, or shortly after, a general election,” said Gover.