The government has refused to publish their own assessments of the effects of a no-deal Brexit for some time, so the serious leak in today's Sunday Times will be a great embarrassment for Boris Johnson.
Just one in five people (19%) believe Mr Johnson will manage to negotiate a fresh deal, while only 7% want an extension to Article 50 to be used to try to reach a deal, suggesting many people think it's unlikely.
However, the threat of a hard border in Ireland highlighted in the document will focus minds ahead of talks between Johnson and European leaders, scheduled for Wednesday and Thursday.
It comes as Boris Johnson will tell French and German leaders that there must be a new Brexit deal when he meets them next week.
But Michael Gove, the minister in charge of coordinating no-deal preparations, challenged that, saying that the documents did set out a worst case scenario and that planning had been accelerated in the last three weeks.
Despite the document being dated to earlier this month when Johnson was already in post, the senior No 10 source said: "This document is from when ministers were blocking what needed to be done to get ready to leave and the funds were not available. It has been deliberately leaked by a former minister in an attempt to influence discussions with European Union leaders", said the source, who declined to be named.
The UK government files warned that businesses and the public are largely unprepared for a no-deal scenario and that contingency planning has been hampered by growing "EU exit fatigue".
Meanwhile, the Mail on Sunday reported that Mr Johnson has accused former chancellor Philip Hammond of "gravely damaging" the national interest with his bids to frustrate Brexit.
He added that the backstop - agreed in Theresa May's withdrawal agreement with the hope of maintaining a seamless border on the island of Ireland - was an "insurance policy" created to protect the peace process.
Instead, it is thought the discussions will revolve around next weekend's G7 agenda - with topics including foreign policy, security, trade and the environment likely to dominate.
But Ms Miller said that whilst the Government had given a reassurance that Parliament will not be prorogued, she said she would be seeking further reassurance that MPs would be able to pass legislation to stop a no-deal Brexit.
Labour leader Jeremy Corbyn has asked cross-bench MPs to "back" him to become caretaker prime minister "before it's too late" to avoid a no-deal Brexit, according to The Observer.
But the reports appear to be the latest assessment of the UK's readiness for leaving the European Union with no deal compiled over the last few months and the Sunday Times report a Whitehall source insisting that this is the scenario expected in the event of a no-deal Brexit.