An SNP MP has said there could be a vote of no confidence in the government early next week aimed at replacing Boris Johnson as prime minister.
Stewart Hosie told the BBC such a move may be the only way of avoiding a no-deal Brexit on 31 October.
SNP leader Nicola Sturgeon hinted on Friday she might back Jeremy Corbyn becoming a “caretaker” prime minister.
The Liberal Democrats have, however, said Mr Corbyn is too divisive a figure to play such a role.
Mr Hosie said opposition parties were in discussions about the timing of a no-confidence vote amid concern that Mr Johnson may find a way of circumventing the so-called “Benn Bill” which requires him to seek an extension to the UK’s departure date if no deal has been agreed.
The aim would be to install an interim prime minister who would secure a short Brexit delay and then call a general election.
“We have to do that because there is now no confidence that the prime minister will obey the law and seek the extension that Parliament voted for only a few weeks ago,” he told the Today programme.
“It we are serious about the extension that is the only game in town.”
In a separate interview on BBC Radio Scotland, he suggested a vote could take place as early as Monday or Tuesday.
Mr Hosie, a former SNP deputy leader, acknowledged that such a plan would need the agreement of opposition parties and Tory rebels in order to succeed.
Liberal Democrat leader Jo Swinson has said an “emergency government” may be necessary but argued that MPs from all parties would not be able to unite around Mr Corbyn as a temporary leader.
She said her party had suggested other MPs as possibilities, including senior MPs who are planning to step down at the next election.
Mr Hosie said: “If another name came forward that was acceptable to everybody, a Ken Clarke or Dominic Grieve-type figure, then self-evidently that would be a good thing to do.” he said.
“But it is also self-evidently the case that the second largest party (Labour) should have the first chance to form that administration.
“If Jo Swinson and the Lib Dems are actually serious about their stopping Brexit position then they need to stop playing political games, get on board with everybody else.”
A motion of no confidence in Parliament allows MPs to hold a vote on whether they want the government to continue.
If the government loses the vote, MPs have 14 days to express their support for an alternative government.
If an alternative government cannot command a majority in the House of Commons in that time, a general election could be held.
Mr Hosie stressed it was vital that opposition parties had a plan in place to secure a Brexit extension before triggering a no-confidence vote.
“If that is not in place and effectively pre-agreed, then we might end up having the general election on Boris Johnson’s terms and allowing him to run down the clock and crash out without a deal.”
For Labour, shadow communities secretary Andrew Gwynne said he did not know whether there would be a confidence vote.