Boris Johnson set out a new ultimatum on Thursday night to MPs: back a general election before Christmas in exchange for more time to scrutinise the Brexit deal.

What exactly has Boris Johnson offered?

In a letter to Jeremy Corbyn, he sought to present himself as open to compromise by telling the Labour leader that he would, after weeks of rancour, give parliament “all possible time” – including late and early finishes and weekend sessions – to scrutinise his withdrawal agreement bill, and aim to ratify it by 6 November.

Whether the bill passes or not, he says, the arrangement would require Corbyn to agree to dissolve parliament immediately and hold an election on 12 December. His letter says that he expects Brussels to now grant an extension until 31 January.

“You have repeatedly said that once the EU accepts parliament’s request for a delay until 31 January, then you would immediately support an election,” he writes. “I assume this remains your position and therefore you will support an election next week.”

Why?

Because he thinks that if Corbyn accepts, the move will give him the best chance of securing a Brexit deal and winning a subsequent election – or failing to get a deal but winning an election by casting Corbyn as the obstacle. Even if Corbyn rejects the offer, Johnson will calculate that Downing Street will again be able to present a “people vs parliament” dichotomy to the public.

How would such a deal be done?

Under the Fixed-term Parliaments Act, two thirds of MPs would have to back a motion asking for an early general election. The motion will be tabled on Monday.

How has Labour responded?

Labour appeared poised to reject the bill, with Corbyn immediately saying that he would not support an election until a no-deal Brexit was “off the table”. But there will be no formal decision from the frontbench until Friday morning. Several shadow cabinet members are said to be minded to reject Johnson’s offer, arguing that 6 November is an artificial deadline for the withdrawal agreement bill. Backbenchers are also said to be anxious about a winter election. But the Momentum campaign group urged the party to back an election, saying: “Bring it on.”

If it does reject the offer, Labour is likely to argue that Johnson is simply trying to distract from his failure to achieve his “do or die” 31 October Brexit promise and seek to portray Johnson as serially dishonest and impossible to trust on Brexit.

What about Brussels?

Sources said that while the significant changes would need to be digested, they could easily alter plans for an extension – which could now be put on hold until the next steps in Westminster have been clarified.

What will happen if the offer is rejected?

Downing Street sources say that they will pull the withdrawal agreement bill to deny MPs the chance to scrutinise it. And they will simply raise the idea again day after day – calculating that parliamentary paralysis will eventually force Labour to concede that an election is inevitable.