Ian Blackford has written to the Prime Minister calling for MPs to gather at the weekend to debate any extension to Article 50 that she secures from EU leaders at a summit in Brussels.
Parliament has only sat on a Saturday four times since the outbreak of the Second World War, including during the Suez crisis and the 1982 conflict with Argentina.
Mr Blackford also stepped up his rhetoric around a second Scottish independence referendum again yesterday, saying he understood the “frustration” of Nationalists putting pressure on Nicola Sturgeon to call a new vote.
The SNP Westminster leader said that with a possible no-deal Brexit just eight days away, MPs should “have the opportunities that we had at the time of the Suez crisis… to ensure that we can stand up for our constituents and protect our people from the catastrophe of no deal”.
“We are in a constitutional crisis,” Mr Blackford said. “We need to reflect on the fact that we are a week away from the intended departure date from the European Union.
“The threat of no deal from the government is very real and we ought to be aware of the consequences.
“The government have told us about the threat to the supply of medicines, to food supplies and to public order.”
Speaking shortly before his appeal in the House of Commons, Mr Blackford said the prospect of a no-deal exit “absolutely scares the living daylights out of me”.
Opposition parties including the SNP and the Liberal Democrats have said that if a no-deal is imminent and there is no prospect of a second EU referendum, they will push for a vote on the “handbrake” of revoking Article 50 outright.
“We know that is a mechanism that is available for the UK to use unilaterally because Scottish politicians prosecuted that case at the European Court of Justice,” Mr Blackford said. “We would have to take our responsibilities.”
With the Prime Minister telling MPs yesterday she would never allow Brexit to be stopped outright, Mr Blackford added: “For a government to ignore, the express opinion of the House of Commons in using the handbrake of revoke to avoid no deal would really put us in uncharted territory. I’d almost be lost for words. This government tells us about the sovereignty of Parliament and to wilfully ignore the will of Parliament would be extraordinary.”
Earlier at Prime Minister’s Questions, Mr Blackford said: “The Prime Minister has failed, this place has failed and Scotland is watching… the people of Scotland deserve a choice on the future and if Westminster fails, Scotland will act.”