Boris Johnson has faced renewed pressure to recall Parliament after the Prime Minister was forced to reveal that a no-deal Brexit could trigger medical shortages, food price rises and major cross-channel trade delays.
The opposition seized on the release of Operation Yellowhammer assessments of the impact of leaving the EU without an agreement to insist MPs return to Westminster.
It comes after Scottish judges branded the suspension of Parliament “unlawful”.
While releasing analysis on impacts of no deal, the Government refused to comply with a similar Commons demand to make public personal messages from special advisers regarding the controversial five week prorogation of Parliament.
The move came as judgment was due on Thursday in a legal challenge that argued the Government’s Brexit strategy will damage the Northern Ireland peace process.
The “reasonable worst case planning assessments” of a no-deal exit which were released at the demand of MPs showed that major hold-ups at channel ports could occur, along with “significant” electricity price rises and a return to a hard border in Northern Ireland.
On food, the document warned that some fresh supplies will decrease and that “critical dependencies for the food chain” such as key ingredients “may be in shorter supply”.
It said these factors would not lead to overall food shortages “but will reduce the availability and choice of products and will increase price, which could impact vulnerable groups”.
The document also said: “Low-income groups will be disproportionately affected by any price rises in food and fuel.”
The analysis said the flow of cross-Channel goods could be reduced to 40% of current rates on day one, with “significant disruption lasting up to six months”.
“Unmitigated, this will have an impact on the supply of medicines and medical supplies,” it said.
“The reliance of medicines and medical products’ supply chains on the short straits crossing make them particularly vulnerable to severe extended delays.”
The document said: “There are likely to be significant electricity (price) increases for consumers.”
The release came after the Court of Session in Edinburgh found ministers had stopped MPs from sitting for the “improper purpose of stymying Parliament”.
It said advice given by ministers to the Queen which led to the five-week prorogation was therefore “unlawful and is thus null and of no effect”.
The Government immediately announced it was lodging an appeal against the ruling with the Supreme Court, with a hearing set for Tuesday.
The document’s assumptions are “as of August 2” this year, and it notes that day one after the scheduled EU exit on October 31 is a Friday, “which may not be to our advantage” and may coincide with the end of the October half-term school holidays.
It added: “Protests and counter-protests will take place across the UK and may absorb significant amounts of police resource.
“There may also be a rise in public disorder and community tensions.”
The Government dossier said that on day one of a no-deal Brexit “between 50-85% of HGVs travelling via the short Channel Straits may not be ready for French customs.
“The lack of trader readiness combined with limited space in French ports to hold unready HGVs could reduce the flow rate to 40-60% of current levels within one day as unready HGVs will fill the ports and block flow.
“The worst disruption to the short Channel Straits might last for up to 3 months before it improves by a significant level to around 50-70%.”
The partly redacted document says UK citizens travelling to and from the EU “may be subject to increased immigration checks at EU border posts” causing delays.
On Northern Ireland, the analysis indicated that the aim of avoiding a hard border may be “unsustainable”.
No deal could also “significantly” impact adult social care providers due to increasing staff and supply costs.
The document is very similar to one leaked last month, which the Government insisted was out of date.
The leaked information was marked a “base case” scenario, but the information released by the Government, part of which was redacted, was labelled a “worst-case scenario”.
Shadow Brexit secretary Sir Keir Starmer said: “These documents confirm the severe risks of a no deal Brexit, which Labour has worked so hard to block.
“It is also now more important than ever that Parliament is recalled and has the opportunity to scrutinise these documents and take all steps necessary to stop no deal.”
The document was released following a Commons motion, but a motion demanding the release of personal information was attacked by the Government.
In a letter to former attorney general Dominic Grieve, Chancellor of the Duchy of Lancaster Michael Gove, who is overseeing no-deal planning, said the Government was opposed to releasing electronic communications issued by named civil servants and Government special advisers regarding the suspension of Parliament.
The Minister said: “To name individuals without any regard for their rights or the consequences of doing so goes far beyond any reasonable right of Parliament under this procedure.
“It offends against basic principles of fairness and the civil service duty of care towards its employees.”
Mr Grieve said: “Even a partial release of the Yellowhammer documents is enough to show how deep the damage a no-deal exit from the EU would do.”