What is the law?

The timing of an election is governed by two laws. One is the Electoral Registration and Administration Act 2013, which sets the minimum period for an election campaign at 25 working days. That means there have to be five weeks between calling an election and polling day.

The other is the Fixed-term Parliaments Act 2011 which sets the date of the next election as 5 May 2022 unless one of two things happens. One is that MPs vote by a two-thirds majority to hold an early election, as they did in 2017.

The other is that the government is brought down by a vote of no confidence, in which case an alternative government can be formed within 14 days (including weekends). If an alternative government doesn’t succeed in carrying a motion of confidence in that time, there must be an election – on a date nominated by the outgoing prime minister.

So there is time before October 31, the Brexit deadline?

If Boris Johnson asked parliament on 19 September for an election on 24 October – the last Thursday before the expiry of the Brexit extension – it could happen if two-thirds of MPs vote for it.

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In 2017, Theresa May was unsure that Labour MPs would vote for an early election. (As it happened, Jeremy Corbyn agreed straight away and most Labour MPs, some of them in tears, voted for it.)

So she allowed an extra two weeks, in case she needed to pass an act to amend the Fixed-term Parliaments Act – which would require a simple majority in the Commons, but would need more time to pass through the House of Lords.

If Johnson were uncertain about a two-thirds majority, he might similarly allow extra time – although an act could also amend the Electoral Registration and Administration Act to shorten the five-week election period.

You mean Boris Johnson could just change the law?

Given that a government with a majority of one in the Commons (which is what Johnson is likely to have after the Brecon and Radnorshire by-election next week) can change the law, the election timetable could be made shorter. This would, however, require the House of Lords to agree, even though the upper house tends not to stand in the way of a Commons majority in such matters.

It is possible that Johnson could pass a law to amend the two Acts to hold an election within, say, three weeks – 17 working days used to be the minimum period for a campaign before 2013. It might even be possible to call an election if parliament, after its break for party conferences, returned on 7 October (these dates have not been fixed yet). There is no legal requirement to hold elections on Thursdays, so it could be, for example, on Monday 28 October.

Needless to say, none of this is very likely.

Could Jeremy Corbyn force an election?

The opposition could force a general election only by bringing down Johnson’s government. Corbyn would have to pass a motion of no confidence and wait for 14 days.

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That process would normally have needed to start on 25 July, the last day before the summer recess, by tabling the motion of no confidence (it requires one sitting day’s notice), to be voted on on 3 September, the day parliament reconvenes after the summer recess.

The only way it could work now would be if the election were held on a day other than Thursday, in the week before 31 October. And there is still a flaw with this plan, which is that Johnson would advise the Queen on which day the election should be held. He could suggest 7 November, ensuring that the UK left the EU without a deal.

What would have to happen, therefore, is that the opposition parties and Conservative rebels would have to agree on a temporary prime minister, such as Kenneth Clarke, to take over for one day during the 14-day period. This temporary government could then use one of the methods above to hold an election on 28, 29 or 30 October.

What is the point?

It has been suggested that Boris Johnson will be unable to get a revised deal through parliament – certainly not by the end of October – and that parliament will block a no-deal Brexit; so he needs to have an election to secure a mandate for his Brexit.

But a “leading Number 10 figure” tells James Forsyth of The Spectator that “there’s no plan for an election”, and “the focus is on leaving on 31 October without a general election”.

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Certainly Johnson’s public position is that he wants a deal, and an election would leave little time to negotiate one.

Jeremy Corbyn, on the other hand, is unlikely to be able to force an election before 31 October. He has no chance of bringing down Johnson’s government until potential Conservative rebels are staring a no-deal Brexit in the face.

Only then is it possible to imagine a scenario in which Labour might help install a temporary prime minister, to agree a Brexit extension and possibly to trigger an election.

If Johnson has failed to secure a Brexit deal, he could pre-empt such a plan by going for an election himself.