MPs who want to stop a no-deal Brexit will seek to bring forward legislation against it this week, shadow Brexit secretary Sir Keir Starmer has said.
He said the plan was to prevent the PM “from taking us out of the EU without a deal” but he did not go into detail.
Cabinet minister Michael Gove refused to guarantee that the government would abide by it if it passed, saying: “Let’s see what the legislation says.”
The government is “not doing anything to facilitate a no deal”, he said.
Meanwhile, the EU’s lead Brexit negotiator has rejected Boris Johnson’s demands for the controversial Irish backstop to be scrapped.
The UK is due to leave the EU on 31 October, with or without a deal.
Sir Keir told the BBC’s Andrew Marr Show: “The legislation is intended to ensure we don’t leave without a deal, that will require an extension.
“The length of the extension is secondary, frankly. We have simply got to stop us leaving without a deal.”
Labour’s shadow chancellor John McDonnell told Sky’s Sophy Ridge on Sunday that a cross-party group that includes MPs and legal experts is looking at introducing a legislative measure next week to stop a no-deal Brexit without parliamentary approval.
“The technique of that will be published on Tuesday, and I’m hoping that we’ll have a debate in which we can bring the House together,” he said.
He said the “ultimate goal this week” was to “ensure Parliament can have a final say”.
But when asked if the government would abide by legislation preventing a no-deal Brexit, Mr Gove, the Chancellor of the Duchy of Lancaster, told the BBC’s Andrew Marr Show: “Let’s see what the legislation says.
“You’re asking me about a pig in a poke.
“And I will wait to see what legislation the opposition may try to bring forward.”
‘No food shortage’
Pressed on whether there would be shortages of fresh food in a no-deal Brexit scenario, Mr Gove said: “Everyone will have the food they need.”
He added: “No, there will be no shortages of fresh food.”
When asked if food prices would increase, Mr Gove replied: “I think that there are a number of economic factors in play.
“Some prices may go up. Other prices will come down.”
He said that freedom of movement will end “as we understand it”, but added that the EU resettlement scheme was “working well”.
The prime minister says he wants to leave the EU on 31 October with a deal, but it is “do or die” and he is willing to leave without one rather than miss the deadline.
That position has prompted a number of opposition MPs to come together to try to block a possible no deal.