Boris Johnson could soon be forced to resign as prime minister and make way for Jeremy Corbyn

• UK prime minister Boris Johnson is quickly running out of options after opposition parties agreed to veto his request for an October election.
• The agreement means that Johnson is likely to soon face a choice between breaking his promise to take Britain out of the EU by the end of October, or stepping down as prime minister.
• Johnson's resignation would leave opposition parties the opportunity to appoint a caretaker prime minister who would be charged with delaying Brexit before calling a general election.
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Boris Johnson could soon be forced to resign as prime minister. Here's why.

Johnson became prime minister back in July on a promise of taking the UK out of the EU on October 31 with or without a deal.

However, this week that plan collapsed after opposition members of parliament passed a new law which is designed to force Johnson to seek a three-month delay to Brexit.

Johnson immediately tried to overturn this by forcing an early general election before Britain's planned exit date from the EU. However, on Friday opposition parties agreed to veto Johnson's request when he makes it for a second time next Monday.

This means that Johnson's plan has all but run out of road and he is likely to soon face a simple, but terrible, choice between two options - neither of which are good.

1. Break his promise to deliver Brexit on October 31.

Opposition members of parliament this week passed a law, which when it receives Royal Assent on Monday, will force whoever is prime minister on October 16 to request a three month delay to Brexit. Without an early election, Johnson has no hope of overturning this law meaning that, if nothing else changes, he will be legally obliged to break his promise to take Britain out of the EU "do or die," on October 31.

Doing so would risk a collapse in his support among Brexit voters and could even lead to a leadership challenge against him from within his own party.

Because of this risk, Johnson has repeatedly insisted that there are "no circumstances" under which he would seek a delay to Brexit, saying on the campaign trail on Thursday that he would sooner "die in a ditch" than comply with the law. This means he only really has one other option.

2. Resign as prime minister.

If opposition parties refuse to give Johnson an October election and if he decides he cannot break his promise to deliver Brexit, then Johnson very quickly runs out of other options. Earlier this week one senior minister briefed the Times newspaper that under those circumstances he would opt instead to resign as prime minister. His official spokesperson on Friday repeatedly refused to rule this out when asked by journalists at a regular briefing in parliament.

Under this scenario Johnson would step down as PM and make way for opposition parties to seek to form a government instead. Due to the defection of Conservative MP Philip Lee and Johnson's decision to oust 21 Conservative members of parliament this week, the prime minister no longer has a working majority in the House of Commons. This means that if Johnson did resign, the queen would have little choice but to look instead to opposition parties to try and form a government instead.

Under this scenario Johnson would then become the leader of the opposition and a new prime minister - drawn from the opposition - would take over.

A caretaker prime minister takes over

As the leader of largest oppostion party, Corbyn would be best-placed to lead this caretaker government. This may prove impossible to agree. Other opposition parties are reluctant to make him prime minister, even temporarily. However, they could in theory agree to do so if he committed to calling an election as soon as he had secured an extension to Brexit, as he has already offered to do. Alternatively, Corbyn could agree to allowing another opposition politician to fill the role instead.

This would be an utterly extraordinary series of events and in ordinary times would be dismissed as mere fantasy.

However, these are not ordinary times and such an outcome could potentially work for both Johnson and Jeremy Corbyn.

For Corbyn, this scenario would allow him to prevent a no-deal Brexit and potentially become prime minister, before going into a general election in which he would hope to win.

For Johnson, it would allow him to avoid breaking his promise, while blaming Labour for the delay to Brexit. He would also then be in a good position to win the next election.

So could this be where the UK ends up in the next few weeks? We will find out very soon.

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