BRUSSELS (REUTERS) - European Union envoys to Brussels will discuss on Friday (Oct 25) the length of another delay to Brexit, with an official from the bloc saying the choice was between three months and a "two-tier" lag but warning that a decision might not come just yet.

According to a draft decision by the 27 EU countries staying on together after Brexit, which was seen by Reuters on Thursday evening, the third postponement would be granted by the bloc "with the view to allowing for the finalisation of the ratification" of the divorce agreement sealed between the bloc and British Prime Minister Boris Johnson last week.

While the draft text, which will be debated in Brussels on Friday, for now leaves the new Brexit date blank, it said the split could take place earlier if ratification is completed earlier - an idea known as "flextension", an amalgamation of the words "flexible" and "extension".

"Consequently, the withdrawal should take place on the first day of the month following the completion of the ratification procedure, or on (blank), whichever is earliest," it read.

The EU official explained: "It's basically between a three-month flextension or a two-tier one."

Under the first idea, Britain would leave on Jan 31, 2020, three months after the current departure date due on Oct 31. The second one would include a second specific date when Britain could leave.

But the person added, under condition of anonymity: "It's unclear if a decision can be taken tomorrow... some might want to see the result of the early election motion."

Mr Johnson on Thursday challenged the factious House of Commons to call an early election on Dec 12 and the chamber is due to vote on that on Monday.

French President Emmanuel Macron has previously managed to sway the bloc's extension decisions significantly from the plans prepared in advance of the bloc's meetings and the line Paris would take is another risk factor on Friday.

A second EU official said: "We'll see tomorrow. Might also be an argument for waiting one day more to see what happens in London."

A third one added: "If there are elections in the UK, it is clear to everybody that we need to give Britain a long extension."

The draft text also said "the further extension cannot be allowed to undermine the regular functioning of the (European) Union and its institutions", a clause the bloc hopes would shield its vital interests from the protracted Brexit drama.

More than three years since Britons voted out, the fate of Brexit remains uncertain, ranging from a disorderly split at the end of this month, to another delay and a national election in bitterly divided Britain.