Next week could be MPs' "only opportunity" to challenge a no-deal Brexit, ex-minister David Gauke has said.
This follows the prime minister's decision to suspend Parliament in September and October.
A statement from opposition parties accused the PM of shutting down Parliament with "the sole aim" of stopping MPs from preventing a no deal.
Leader of the House Jacob Rees-Mogg said outrage at the plan was "phoney".
The government said the five-week suspension - known as prorogation - in September and October will still allow time to debate Brexit.
But government whip Lord Young has resigned in protest, arguing the move risks "undermining the fundamental role of Parliament".
And a Scottish court hearing is under way which could block the suspension of Parliament.
Former justice secretary David Gauke told the BBC the public did not want a no-deal Brexit, but that the options of those opposed to such an exit have "now narrowed".
"That would suggest we need to move sooner rather than later," he said.
And shadow chancellor John McDonnell said he believed that Parliament would be able to find a way to stop a no-deal Brexit but that nobody should "underestimate" how difficult it would be.
A video has emerged of Defence Secretary Ben Wallace discussing the PM's decision to suspend Parliament with the French defence minister Florence Parly.
He can be heard saying that Parliament had been "very good at saying what it doesn't want, but… awful at saying what it wants".
What might happen next?
Despite having little time, MPs still have options for trying to block a no-deal Brexit.
They could try to take control of the parliamentary timetable in order to pass legislation which would force the PM to request an extension to the Brexit deadline.
Another option would be to remove the current government through a vote of no confidence.
Labour leader Jeremy Corbyn said opposition MPs would take the first steps towards trying to pass a law blocking a no-deal Brexit when Parliament returns on Tuesday.
Asked whether they still had the time to pass such legislation, he replied: "We believe we can do it, otherwise we wouldn't be trying to do it."
He said tabling a no-confidence motion in the PM at an "appropriate moment" also remained an option.
It is also thought some MPs are exploring ways of ensuring Parliament can meet on the Friday, Saturday and Sunday before the planned suspension.
Conservative peer Lord Young of Cookham said in his resignation letter that the timing and length of the suspension "risks undermining the fundamental role of Parliament at a critical time in our history".
Meanwhile, Ruth Davidson has also confirmed she is quitting as leader of the Scottish Conservatives, citing personal and political reasons.
Ms Davidson - who backed Remain in the 2016 EU referendum - added she had never sought to hide the "conflict" she felt over Brexit, and urged Mr Johnson to get a Brexit deal.
What was decided?
On Wednesday, Mr Johnson said a Queen's Speech would take place after the suspension, on 14 October, to outline his "very exciting agenda".
Mr Rees-Mogg said this parliamentary session had been one of the longest in almost 400 years, so it was right to suspend it and start a new session.
"The candyfloss of outrage we've had over the last 24 hours, which I think is almost entirely confected, is from people who never wanted to leave the European Union," he told BBC Radio 4's Today programme.
But Ruth Fox - director of parliamentary experts the Hansard Society - said this prorogation was "significantly longer than we would normally have" for the purpose of starting a new parliamentary session.
Ms Fox said that depending on the day the suspension began - and on whether MPs would have voted to have a party conference recess at all - the prorogation could "potentially halve" the number of days MPs have to scrutinise the government's Brexit position.
The prime minister says he wants to leave the EU at the end of October with a deal, but is willing to leave without one rather than miss the deadline.
In a joint statement from Labour, the SNP, the Lib Dems, Plaid Cymru, the Independent Group for Change and the Green Party, the parties condemned the "undemocratic actions" of the prime minister.
The parties also called on Mr Johnson to reverse his decision "immediately" or allow MPs to vote on the suspension.
Others, though, have defended the plan.
Former Cabinet Office minster Damian Green tweeted that there was time to ratify a deal with the EU before 31 October, saying: "This is all normal Parliamentary democracy, which shows that the talk of coups and dictatorship is massively overblown."
The leader of the DUP, Arlene Foster, also welcomed the decision, but said the terms of her party's agreement with the Conservatives would now be reviewed.
Earlier, hundreds of protesters gathered outside the office of Tory MP Alex Chalk in Cheltenham.
Mr Chalk - who is the Parliamentary Private Secretary to Foreign Secretary Dominic Raab - told his constituents the message sent out by proroguing Parliament was "wrong" and he didn't think it was "the right thing to do".
He said he had "always" been in favour of a "compromise solution" and warned those who "insist on absolute victory risk absolute defeat".
Protests are expected around the country into the weekend.
Meanwhile, an e-petition on the government's website demanding Parliament not be suspended reached more than 1.5m signatures.
A snap YouGov poll conducted on Wednesday suggested 47% of British adults thought the decision was unacceptable, with 27% saying it was acceptable and 27% unsure.
But it suggested the suspension was supported by 51% of people who voted Leave, with 52% of Conservative voters also approving of the move.
What about the legal challenge?
Scotland's top civil court is considering a challenge to the suspension of Parliament, led by the SNP's justice spokeswoman, Joanna Cherry.
The judge will consider overnight whether to grant the Scottish legal equivalent of an injunction to stop it - pending a full hearing on 6 September - and is expected to return to court to give his decision at 10:00 BST on Friday.
It is not possible to mount a legal challenge to the Queen's exercise of her personal prerogative powers.
Campaigner Gina Miller has made an application to the Supreme Court, seeking permission for a judicial review of the PM's decision.
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