The European Union is set to step up discussions on Friday over the length of another Brexit delay in the wake of British Prime Minister Boris Johnson's call for a December 12 election.

A House of Commons vote on an election is due on Monday, and the EU decision on an extension, initially expected on Friday, may now be delayed until after the weekend. 

The timing of the EU's decision will be critical, with support for an early election from opposition parties unrealistic if a three-month extension is not in place. 

Johnson's election gambit

Johnson on Thursday challenged the House of Commons to back a general election, saying he would give time for further scrutiny of his Brexit deal up to November 6 in exchange for a poll on December 12.

"If they [MPs] genuinely want more time to study [the Brexit deal] they can have it, but they have to agree to a general election on December 12," Johnson said. "That's the way forward."

Johnson said MPs could have as much parliamentary time as they wanted up to November 6, but if his Brexit deal had not been passed by then he would campaign for it in a December election and pass it into law if he won a majority.

The election call is an admission the prime minister's pledge to guide the UK out of the EU "do or die" by October 31 will almost certainly not be delivered, though there remains a slim chance he will again try to pass his Brexit deal before the end of the month. 

Can PM force an election?

Johnson will attempt to force an early election via the Fixed-term Parliaments Act, but requires the backing of 434 MPS – two-thirds of the House of Commons – to succeed. Whether an election is approved will depend on opposition parties, with Labour split over backing a December contest. 

Jeremy Corbyn, the Labour leader, has said he would support an election when a no-deal Brexit was "off the table" – assumed to mean if a three-month extension to the Brexit deadline is granted, given the only ways to permanently rule out a no-deal exit would be to pass a deal or cancel Brexit.

However, at least half of Labour's MPs are thought to be opposed to an election before the first stage of Brexit is settled and Corbyn would risk a damaging split if he were to push his party to vote for a new poll.

Labour could face pressure from the Scottish Nationalists and Liberal Democrats however, both of which have indicated they may vote in favor of an election if the EU extends the Brexit deadline to January 31

What will the EU do?

EU envoys to Brussels are scheduled to discuss on Friday the length of another delay to Brexit, with an official from the bloc telling Reuters the choice was between January 31 and a "two-tier" proposal but warning that a decision might not come until after the weekend.

The EU source told Reuters: "It's unclear if a decision can be taken tomorrow (Friday) ... some might want to see the result of the early election motion.”

The timing of an extension decision from the EU will be key to the outcome of Monday's election vote, given there's little chance of opposition parties backing an election before the length of any extension is confirmed.

(CGTN Europe's Alex Hunt contributed to this article)