An explosive set of leaked emails has shown DUP leader Arlene Foster preparing for a no-deal Brexit as the most likely outcome after frayed negotiations this week with the EU.
In the exchange between senior UK officials, seen by The Observer, Mrs Foster envisaged a no-deal Brexit as the "likeliest outcome".
The DUP leader last week met with the EU's chief Brexit negotiator Michel Barnier to discuss Northern Ireland's post-Brexit future.
The issue of the 'backstop' to avoid a hard Irish border has plagued negotiations.
The EU favours a potential backstop arrangement which would see customs remain aligned between Northern Ireland and the EU - which the DUP stridently opposes.
In the leaked email exchange, an adviser involved in the Brexit talks described Mrs Foster's comments during a meeting with the leader of the Conservative MEPs, Ashley Fox.
"She described Barnier as being difficult and hostile in her meeting today…" the leaked exchange reads.
"AF (Arlene Foster) said the DUP were ready for a no-deal scenario, which she now believed was the likeliest one."
It is also noted that it was not clear whether the DUP leader was threatening to end the 'confidence and supply' deal with the Conservative Government, or was simply making her plans clear.
Elsewhere, former Foreign Secretary Boris Johnson, writing in the News Letter, said: "The only way to put things back on the right track is to ditch the backstop and then to chuck Chequers."
He warned that the UK faced its "greatest national humiliation since Suez", adding: "We will be heading for colony status, with many laws imposed on us, with no control over our trade, and with internal checks at the behest of a foreign power."
Meanwhile, two former Secretaries of State are among 63 Conservative MPs who have signed a letter attacking the Government over its Brexit forecasts.
The letter from Tory backbenchers represents yet another challenge to Prime Minister Theresa May's authority. The Eurosceptic MPs have blamed the Government for leaking negative Brexit forecasting and insist that Chancellor Philip Hammond must release information about the modelling it uses.
Owen Paterson and Theresa Villiers are among the signatories on the letter, alongside Conor Burns, a Northern Ireland-born Conservative MP; David Davis, the former Brexit secretary; hardline Brexiteer Jacob Rees-Mogg, and the former Brexit Minister Steve Baker.
A number of Conservative donors and leading businessmen also put their names to the letter, including Belfast-born Tim Martin, the founder and chairman of the pub chain JD Wetherspoon.
The MPs have all urged the Government to publish in full detail the cross-Whitehall Brexit analysis and the underlying models so that experts from all sides can study its methodology, assumptions and conclusions.
"It is unacceptable that the Government leaks the results of its modelling when it suits but simultaneously hides what lies behind these forecasts from the public," the letter said.
"While all such forecasts are only indicators of orders of magnitude and general direction, independent private sector forecasts and those of Whitehall are wildly far apart, many of which forecast a positive impact on GDP.
"Such differences have huge consequences for Brexit strategy and the long-term trajectory of future public expenditure, taxation, and borrowing."