The deadline imposed on Boris Johnson by Parliament for securing a deal with the European Union should be brought forward, according to the Liberal Democrat leader.
Jo Swinson said she will not support a no confidence vote in the Prime Minister until a no-deal Brexit has been removed as a possibility.
The so-called Benn Law – legislation passed by the Commons earlier this month to prevent leaving without a deal – gave the Conservative Party leader until October 19 to secure a deal or else face having to ask Brussels for a three-month extension to the talks.
But Ms Swinson said she wanted to “bring forward” that cut-off date to ensure there was time to legally challenge Mr Johnson to comply with the law.
Mr Johnson has previously said he would rather be “dead in a ditch” than write to European leaders requesting an extension to Article 50 beyond the current formal Halloween deadline.
Addressing the media outside Parliament, Ms Swinson argued that a 12-day buffer between the Benn Law deadline and October 31 was not enough to safeguard against no deal.
If Mr Johnson refuses to comply with the law and request an extension by October 19, the courts could force him to act – but Ms Swinson warned that such a process “takes time and there are risks attached to it”.
“We would argue that 12 days is not sufficient, particularly in line with a Prime Minister who has shown he is prepared to disobey the law,” she said, standing in front of Lib Dem MPs and peers.
“Even with the Supreme Court judgment, he has talked about disagreeing with it as if a Supreme Court judgment is something you can pick and choose whether or not it is right.
“That is why we have to bring forward the ways in which we can make sure the no-deal threat is removed.”
The former coalition minister ruled out pushing for a vote of no confidence in the Government until that deadline is moved.
“Our country is in a moment of great peril and it is hugely important that we do not risk accidentally crashing out of the European Union, and that is the risk of an early vote of no confidence,” said Ms Swinson.
“That is why we are saying we should explore all options to bring forward that guarantee that we can take no deal off the table because then we can get rid of this Prime Minister, who is unfit for office.
“We saw in September the House of Commons take control of the order paper to pass a piece of legislation and that’s the type of way forward that may well enable us to take the threat of a no-deal Brexit off the table much sooner than October 19.”
Labour leader Jeremy Corbyn said similarly on Wednesday that taking no deal off the table remained his “priority” rather than toppling Mr Johnson.
Mr Corbyn told BBC Radio 4’s Today programme: “Until it is very clear that the application will be made, per the legislation, to the EU to extend our membership to at least January, then we will continue pushing for that and that is our priority.”
He added: “When that has been achieved, we will then be ready with a motion of no confidence.”