EU leaders have agreed to grant a Brexit extension until January 31 2020, with the option for the UK to leave earlier if a deal is ratified.
Donald Tusk, the president of the EU Council, announced the decision on Twitter on Monday morning following a meeting of ambassadors.
Boris Johnson has previously said he would prefer to be “dead in a ditch” than accept a delay to Brexit beyond October 31.
But the prime minister was forced by parliament to ask for an extension to the Article 50 process amid concerns by MPs he could take the UK out of the EU with no-deal at the end of this month.
The announcement will pile pressure on opposition parties to decide whether to back a pre-Christmas general election, with MPs voting later on Monday on a government bid to hold a poll on December 12.
Labour has said it will only back the move if Johnson makes “absolutely clear” that no-deal is off the table and a January extension is granted.
But the Liberal Democrats and SNP have put forward a tightly-drafted Bill that would grant an election on December 9 – three days earlier than the PM’s suggested polling date – as long as the European Union grants an extension until January 31.
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The prime minister’s election bid on Monday, to be made under the Fixed-Term Parliaments Act (FTPA), would require a two-thirds Commons majority – 434 MPs – to agree to an election on December 12.
Lib Dem leader Jo Swinson said her proposal ties Johnson’s hands over the election date and does not give him the “wriggle room” that his own plan would have.
“And because people can’t trust what this man says, I think setting that date in law is a very good idea,” she told Today.
The draft SNP-Lib Dem law, currently scheduled for Tuesday’s sitting, would require a simple majority of 320 MPs to support it in order to dissolve parliament – 114 fewer than under the FTPA “super majority” rules.
With the SNP and Lib Dems supporting the initiative, the bill is likely to pass even without Labour backing.
Downing Street indicated it could be willing to support the pro-Remain parties’ proposals in a possible compromise offer.
If passed, the SNP-Lib Dem Bill is likely to achieve Royal Assent by Thursday and parliament would be dissolved by the end of the week for the first December poll in almost a century.
Its quick dissolution turnaround period would mean the Withdrawal Agreement Bill – the attempt to put Johnson’s Brexit deal with the EU into law – would fail to pass before Halloween.