Jeremy Corbyn has issued an urgent plea to MPs to unite to stop no-deal Brexit “before it’s too late”, amid cross-party demands for an immediate recall of parliament to deal with the crisis.

In a show of defiance, a group of more than 100 MPs representing every Westminster party except the DUP has signed a letter stating it is “unacceptable” for parliament to wait until next month to sit again, with the Brexit deadline looming.

Labour and Tory MPs plot ‘radical’ law to thwart no-deal Brexit Read more

The call comes with more Tory MPs opposed to leaving without a deal making clear that they will not back Corbyn’s offer of heading a temporary government that is committed to delaying Brexit and calling an election. Corbyn told the Observer that MPs were flirting with disaster.

“My message to MPs across parliament is simple and urgent: only by working together can we stop no deal,” he said. “Three years after the EU referendum, the country stands at a precipice. Boris Johnson has become prime minister without any popular mandate. He has no right to drive our country off a cliff and into the arms of Donald Trump with his no-deal fixation. The plan I set out last week is the simplest and most democratic way to stop no deal. We have to seize the opportunity before it’s too late, so the people, rather than an unelected prime minister, can decide our country’s future.”

Corbyn’s opponents insist that any temporary government will only gain enough support if it is led by a neutral figure. The former Conservative minister Sir Oliver Letwin, a key figure in parliament directing efforts against a no-deal Brexit, said on Saturday he could not back a Corbyn-led emergency government. It is understood that Richard Harrington, a Tory MP who quit as a minister over Brexit, also feels he could not back a Corbyn-led government.

Facebook Twitter Pinterest Sir Oliver Letwin has said he could not back a Corbyn-led emergency government. Photograph: Dominic Lipinski/PA

Senior MPs are now preparing alternative methods of ensuring parliament can block a no-deal Brexit, but know they face a race against time. The Tory MPs Dominic Grieve and Guto Bebb are among the signatories of a letter, sent to Boris Johnson on Sunday, that calls for him to recall parliament. It accuses him of “creeping and disturbing populism” over his dealings with the EU. Labour’s leadership is also understood to be supportive of the idea of recalling parliament. “Since the second world war, parliament has been recalled multiple times in every decade for a wide range of political, security and economic reasons,” states the letter, co-ordinated by backbenchers Luciana Berger and Stephen Doughty.

It continues: “Our country is on the brink of an economic crisis, as we career towards a no-deal Brexit which will have an immediate effect on food and medical supplies, damage our economy, jobs, the public finances, public services, universities and long-term economic security. A no-deal Brexit also threatens our crucial security cooperation to keep our country safe from criminals and terrorists.

“We face a national emergency, and parliament must be recalled now in August and sit permanently until 31 October, so that the voices of the people can be heard, and that there can be proper scrutiny of your government. A true democrat should not fear such scrutiny. The question is whether you are one.”

According to leaked government documents on “Operation Yellowhammer”, published by the Sunday Times, the “most likely aftershocks” of a no-deal Brexit include the UK being hit with a three-month “meltdown” at its ports, a hard Irish border and shortages of food and medicine after it leaves leaves the bloc.

A senior Whitehall source told the paper: “This is not Project Fear – this is the most realistic assessment of what the public face with no deal. These are likely, basic, reasonable scenarios – not the worst case.”

The report came as attention is turning to the battle to pass a new law forcing Johnson to delay Brexit to avoid leaving without a deal. Allies of Philip Hammond, the former chancellor, are warning Tory MPs not to wait until October to take part in attempts to block no deal. “There are too many Tories thinking, ‘Let’s wait until October, get through party conference and see where we are’,” one said. “We simply cannot afford to do that.”

Campaigners are also claiming an early legal victory. Gina Miller, the businesswoman who won a previous Brexit case, believes government lawyers have conceded that Johnson cannot suspend parliament in order to force through a no-deal Brexit. She argues that, in a letter to her legal team, government lawyers state they cannot prorogue parliament to stop MPs from blocking no deal. The letter states the issue is “entirely academic” because parliament has already voted to ensure it sits in key periods in the run-up to the Brexit deadline of 31 October. “Parliament has ... afforded itself the ability to scrutinise the terms of any exit of the UK from the European Union and to hold the government to account,” the government lawyers state. “There is no question of parliament being denied these functions prior to 31 October 2019.”

Miller’s legal team is seeking further guarantees from the government over its plans. “The clarification in this letter settles much of the debate, and I am delighted this has been achieved without, so far, having to approach the courts,” Miller said. “The government’s carefully worded response does not specify that parliament will have an opportunity to legislate to resist a no-deal Brexit, which ignores the central tenet of our argument that it would be abusive to prevent parliament from doing so.”

But other legal experts say the government has left itself significant wiggle room to prorogue parliament. They also warn that its lawyers have not ruled out dissolving parliament before an election to force a no-deal exit.