Boris Johnson will introduce an “almost identical” bill to the December 9 general election proposal put forward by the Liberal Democrats and the SNP if his own bid for a poll fails, it has been reported.
A Number 10 source told the Press Association that if the government’s plan for a general election on December 12 is rejected by MPs in the House of Commons later on Monday, it will simply copy the two parties’ proposal.
On Monday, in a significant setback to Mr Johnson, the EU agreed to grant a Brexit extension until January 31, 2020.
The prime minister will ask MPs to back his plan for a general election on December 12 in the House of Commons later.
He needs two-thirds of MPs - 434 - to back the government motion for it to pass under the Fixed-Term Parliaments Act (FTPA), but is unlikely to succeed because of Labour opposition.
The SNP and the Liberal Democrats have proposed their own bill, scheduled for Tuesday, which would only need a simple majority of MPs, to have a general election on December 9.
The source said: "Tonight is Labour's last chance to have an election with Brexit done - they can vote tonight for the 12th and get Brexit done before Parliament is dissolved.
"If not, we will introduce a bill almost identical to the SNP bill tomorrow and we will have a pre-Christmas election anyway.”
The Liberal Democrats said they would need to see any Bill brought forward by the government before deciding whether to support it.
One Lib Dem source told the Press Association it had to contain protection against a no-deal break, with the date of the election stipulated in the legislation.
"It is about making sure that Boris Johnson in some cunning fashion cannot engineer a situation where we crash out of the EU without a deal," the source said.
Labour leader Jeremy Corbyn says his party will not support the motion unless the threat of a no-deal Brexit is ruled out.
Mr Johnson could push his own simple majority plan for a general election if he loses the initial vote, knowing he would need 100 fewer MPs to grant the same request.
Mr Johnson has already had two requests for an election refused.
The SNP/Lib Dem draft 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.
If passed on Tuesday, 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 (WAB) - the attempt to put Mr Johnson's Brexit deal with the EU into law - would fail to pass before Halloween.
‘Dead in a ditch’
Earlier on Monday, Brussels accepted the UK's request for a so-called "flextension" until January 31 - enabling Britain to leave the bloc sooner if the WAB becomes law.
The PM had said in the past he would prefer to be "dead in a ditch" than miss the October 31 deadline.
European Council president Donald Tusk announced the decision following a meeting of ambassadors in Brussels.
He said: "The EU27 has agreed that it will accept the UK's request for a #Brexit flextension until 31 January 2020.
"The decision is expected to be formalised through a written procedure."
Britain would be able to leave the EU on the first day of the month following the ratification of the WAB by both the European and UK parliaments.
Scottish First Minister Nicola Sturgeon took to Twitter to explain why the SNP was backing a December 9 election.
She said there was "no evidence" that a majority for a second referendum existed in Parliament and that it would be more embarrassing for the Conservative Party leader to have to fight an election before having delivered Brexit as promised.
"An election now would instead force him to explain his failure to keep his October 31 'do or die' promise and also defend his bad deal," said the SNP leader.
Lib Dem leader Jo Swinson told the BBC's Andrew Marr programme: "We think we need to resolve this impasse. We think the best way to resolve it would be a 'people's vote' but, in the absence of proper Labour numbers to do that, a general election would be the other way."