Opposition leaders trying to block a no-deal Brexit have failed to agree who should lead a unity government if Boris Johnson is toppled.
Jeremy Corbyn is insisting he, as Leader of the Opposition, should take over if the PM is defeated in a vote of no confidence.
But Liberal Democrat leader Ms Swinson, also speaking after cross-party talks on Monday, flatly rejected the possibility that her MPs could back Mr Corbyn as an interim prime minister.
Ms Swinson said party whips would meet to discuss candidates to take over from the Prime Minister if he is ousted, but said the Mr Corbyn cannot command support in the Commons.
“He simply does not have the numbers,” Ms Swinson said, referencing the 21 MPs exiled from the Conservative Party and the five within the Independent Group for Change (IGC).
“I have been crystal clear but I will do so again – Jeremy Corbyn is not going into Number 10 on the basis of Liberal Democrats’ votes.
Parliament has already passed the so-called Benn Act, requiring Mr Johnson to request a further extension to the Article 50 withdrawal process if he cannot get a new agreement by 19 October.
But some on the opposition side fear that could leave too little time to take action through the courts if Mr Johnson tries to circumvent the legislation and push through a no-deal break.
While he has repeatedly said he will abide by the law, Mr Johnson has also insisted the UK will leave the EU on 31 October come what may.
A Liberal Democrat source confirmed Ms Swinson would be putting forward the idea of bringing forward the deadline for seeking an extension when she meets counterparts from Labour, the SNP, Plaid Cymru and the Greens.
“I expect it to be discussed at the meeting. It is certainly Jo’s intention that it should,” the source told the Press Association.
Ian Blackford, the SNP leader at Westminster, signalled his support for the Lib Dem plan, saying he would back any measure which prevented Mr Johnson bypassing the Benn Act.
“All of us have got to work together. I’m not precious. Everyone is much more aware of what he is capable of,” he told The Daily Telegraph.
“There is no doubt that he will seek to frustrate the legislation in place as we head towards the second half of October.”
A Labour source said: “We are looking at all mechanisms and additional legal safeguards to block no-deal and ensure the PM complies with the Benn Act.”
The move could see Tory MPs and ministers forced to abandon their party conference in Manchester and dash back to Westminster if the opposition stage an ambush to seize control of the Commons agenda.
Unusually, the Commons is sitting during the Tory conference after MPs refused to grant the government the customary recess in the bitter aftermath of the Supreme Court ruling that Mr Johnson’s suspension of Parliament was unlawful.
The latest plan comes after the SNP failed to win support for a tabling no-confidence motion with a view to forming an interim government if it succeeded in toppling Mr Johnson.
Under the proposal, the temporary administration would have sought an extension from the EU and then immediately called a general election.
However, the other opposition parties were wary, amid concerns Mr Johnson could have tried to hang on in No 10 and delay an election until after 31 October, by which time Britain would be out.
There are also sharp differences between the parties over who would lead such a government.
Jeremy Corbyn has said that, as the leader of the biggest opposition party in the Commons, he should have first crack at forming an administration – a position broadly supported by the SNP.
However, Ms Swinson has been adamant that she would not be prepared to put the Labour leader in No 10.
Her view is shared by many of the rebel Tory MPs who lost the whip after rebelling over Brexit and whose votes would be needed if the plan was to succeed.
Some MPs have suggested that a more consensual figure such as Ken Clarke or Dame Margaret Beckett could stand a better chance of uniting the parties.
Other ideas floating around Westminster include tabling another bill to enable Commons Speaker John Bercow to seek an extension from Brussels if Mr Johnson refuses to do so.