Labour, the Lib Dems and the SNP appear increasingly at odds over how best to stop a no-deal Brexit, despite efforts to combine forces in Parliament.
Opposition talks on Monday made little headway over when to try and vote down Boris Johnson's government and who might succeed him as prime minister.
Labour said the Lib Dems were being "irresponsible" in refusing to back a temporary Jeremy Corbyn-led government.
But Lib Dem leader Jo Swinson said he did not have wide enough support.
The SNP called on the other two parties to "grow up" and warned that time was running out to stop the UK leaving the EU on 31 October.
Opposition forces in Parliament, including ex-Tory MPs now sitting as independents, have been talking to each for several weeks on how best to guarantee the UK does not leave without a legally-binding agreement at the end of the month.
However, the group - also including the Greens, Plaid Cymru and the Independent Group for Change - have not been able to agree on the timing of any vote of confidence in the Conservative government.
After their latest meeting on Monday, the parties remained at odds over who might replace Mr Johnson if the PM, who does not have a majority in Parliament, is defeated.
If that happened, parties in the Commons would have 14 days to try and form an alternative government or there would be an election.
'Precedence and procedure'
Mr Johnson has said the UK will leave on 31 October with or without a deal - despite a law passed last month requiring him to ask for a further delay if no deal is agreed by 19 October.
The government has said the prime minister - who insists his latest proposals are the basis for an agreement with the EU - will comply in full with the so-called Benn Act.
Monday was originally pencilled in for a Commons ambush - the plan was to pave the way for opposition figures to take control of business from next week to pass more emergency laws on no-deal, or demand more documents in the run-up to 31 October.
But that has now been put on ice.
Sources say former Tory MPs expelled last month for refusing to back Mr Johnson's strategy got cold feet and want to give No 10 more time to try and get a new deal with Brussels.
Those opposition figures who have been frantically trying to get all their MPs to the Commons today are less than pleased.
But many opposition MPs remain concerned the UK could end up leaving without a deal anyway if the government challenges the legislation in court or seeks somehow to nullify it.
The SNP has been pushing for an early vote of confidence to be held in Parliament to bring in a temporary government that will definitely accept a Brexit extension.
But while they are prepared to see Mr Corbyn lead that government, the Lib Dems remain adamant he does not have the necessary support to do so.
They want a "government of national unity" to be led by a respected senior parliamentarian, such as Margaret Beckett or Ken Clarke, who can attract both Labour and Tory support.
"From my perspective that could be anybody who commands the confidence of the House of Commons," Ms Swinson told the BBC on Monday.
"Astonishingly Labour have said they would not back anybody but Jeremy Corbyn.
"If they stick to that position, it will end up being the case that the biggest block to stopping a no-deal Brexit will be Jeremy Corbyn himself."
But senior Labour figures said this was a "destructive" approach.
"We need to be holding Jo Swinson to account as to why she would risk our country crashing out of the EU... rather than follow precedence and procedure and allow Her Majesty's opposition to form a government for a temporary time only," said Dawn Butler.
The shadow equalities minister said there was "no guarantee" any other figure would command the support of MPs, adding that if the Lib Dems were "proved right and Jeremy doesn't have the numbers then we'll consider our next step".
SNP leader Nicola Sturgeon urged them to put their differences aside, saying a Corbyn government would only be in power for a very short time pending a general election.
Both Labour and the Lib Dems need to grow up. Who leads a temporary govt that will be in office for just a matter of days is not the key issue. What matters is getting this Tory government out, securing an extension and then having a General Election ASAP. https://t.co/oOAs2jBw5x— Nicola Sturgeon (@NicolaSturgeon) October 7, 2019