A Cabinet minister has issued the strongest warning yet about the prospect of a united Ireland if there is a no-deal Brexit.
Justice Secretary David Gauke has said he worries "a great deal" about what a crash-out Brexit would mean and that it would put the future of Northern Ireland in the Union "in some doubt".
The remarks are being viewed as a message to the DUP, whose 10 MPs prop up Theresa May's Conservative government.
The DUP has vehemently opposed the Prime Minister's withdrawal agreement due to concerns that the so-called backstop to avoid a hard border in Ireland would threaten the Union with Britain.
Mr Gauke's remarks came ahead of another crunch week where Westminster will again try to seek consensus on alternatives to Mrs May's deal.
He was asked on the BBC's Andrew Marr Show yesterday what a no-deal Brexit would do to the country.
He replied: "I think it would be very, very bad news indeed," citing the economic consequences as well as security concerns.
"I do worry a great deal about what that will do to the integrity of the United Kingdom.
"At the moment moderate nationalist opinion in Northern Ireland is reconciled to its position as part of the United Kingdom."
He said a no-deal scenario would see the UK Government have to impose direct rule and would bring about a situation "where we were essentially heading towards a hard border between Northern Ireland and the Republic of Ireland".
"I think that puts it in some doubt, the future of Northern Ireland's place in the UK," Mr Gauke said.
Last night a DUP spokesperson responded, reiterating the party's concerns about Mrs May's deal.
"A deal which places a trade barrier between Northern Ireland and the rest of the United Kingdom undermines the economic and constitutional integrity of the Union," the DUP said.
"We want a better deal which protects the Union and delivers on the referendum result."
With MPs set to hold a second round of "indicative" votes on alternatives to the Prime Minister's deal today, Mr Gauke said Mrs May would have to "look closely" at any option that could command a majority.
After 170 Tory MPs - including 10 members of the Cabinet - wrote to Mrs May urging her to take the UK out of the EU as quickly as possible, Mr Gauke reiterated he would resign rather than support a no-deal break.
He said that if MPs did coalesce around a plan by veteran Tory Ken Clarke for a customs union - which came closest to securing a majority in the last round of votes - ministers should be prepared to consider it.
However, any move to accept a customs union would infuriate Brexiteers and would almost certainly lead to ministerial resignations.
But Mr Gauke cautioned: "If Parliament is voting overwhelmingly against leaving the European Union without a deal but is voting in favour of a softer Brexit, then I don't think it's sustainable to ignore Parliament's position and therefore leave without a deal."