Jo Swinson has offered to meet with Jeremy Corbyn to discuss ways to block a no-deal Brexit .
But in a letter to Mr Corbyn the Lib Dem leader said she didn’t think a plan to install the Labour leader as a ‘caretaker’ PM was not “viable”.
She said he would not have enough cross party support to take power.
Ms Swinson wrote: “Regardless of how my party were to vote in those circumstances, in order for you to command the confidence of the House, at least eight Conservative MPs would need to support you in taking office.
“For this and other reasons, I do not believe your plan is viable.”
She added: “I would be interested to know whether eight or more Conservative MPs have indicated to you that they will support you in these circumstances.
“However, there are clearly other senior members of the House who could potentially command a majority in the House.
“Today I suggested that Ken Clarke or Harriet Harman, the Father and Mother of the House, could lead an emergency government.”
Jeremy Corbyn sent a letter calling for the other opposition leaders – and some senior Tory backbenchers committed to thwarting no-deal – to help install him as a caretaker leader.
But Ms Swinson initially dismissed Mr Corbyn’s letter calling for parties to work together as a “nonsense”.
Time is running out for any attempt to oust Boris Johnson ahead of no-deal.
And there is concern that the PM could call a general election after the UK has left the EU.
In his letter to the opposition parties Mr Corbyn said he would seek to call a no-confidence vote at the “earliest opportunity when we can be confident of success”.