THERESA May decided against allowing the UK to crash out of the EU without a deal after being warned about the potential for an upsurge in paramilitary violence in Northern Ireland, her de facto deputy has said.
Former Cabinet minister Sir David Lidington, who is standing down as an MP, revealed that the ex-prime minister effectively ruled out a no-deal Brexit after a meeting police chiefs and community groups in Belfast in February.
He told the Sunday Times: "What really struck her was how the prospect of no-deal was driving them towards actively supporting a united Ireland, rather than being content to let sleeping dogs lie."
Sir David said that he did not think friction on the border would cause violence, but that "people who are inclined that way would seize upon any opportunity... because it would be a grievance they could exploit".
"Anything on the border itself - even cameras - was certain to produce an increase in tension. I sat in meetings in Londonderry and in Newry and Co Fermanagh, and I was told that in no uncertain terms."
Britain was due to leave the EU on March 29, but Mrs May twice requested an extension to Article 50 - resulting in her being offered a "flexible extension" to Brexit until October 31.
Meanwhile a business minister has said Boris Johnson was right to claim there would be no barriers to trade crossing the Irish Sea after Brexit.
Kwasi Kwarteng defended the prime minister after he said there would be "no forms, no checks, no barriers of any kind" under his Withdrawal Agreement.
Mr Johnson's comments suggested Brexit Secretary Stephen Barclay had been wrong to say goods between Northern Ireland and the rest of the UK would face checks as a result of the Brexit deal struck with the EU.
But Mr Kwarteng told Sky's Sophy Ridge On Sunday that the PM was "absolutely right" in his remarks.
He said: "I think that the whole point of the deal is that we want to have a frictionless border but at the same time we want to leave the EU...
"From our side we want to have as little bureaucratic interference as possible and I think what the Prime Minister said is absolutely on the money."
He said his understanding was that there would not be exit summary declarations.
Mr Johnson told Conservative supporters and Northern Ireland business figures last week that the secretary of state's advice was not correct.
The Tory leader, in a video shared by Manufacturing NI on Twitter, said there would be "no forms, no checks, no barriers of any kind" as a result of his Withdrawal Agreement.
Mr Johnson was asked by Irwin Armstrong, owner of CIGA Healthcare, whether he could "go back to my company in the morning and tell my staff we will not be filling in any customs declarations for good leaving Northern Ireland to go to GB?".
The PM replied: "You can."
Mr Kwarteng was also asked about Mr Johnson's likening of Labour leader Jeremy Corbyn to Soviet leader Stalin - who persecuted Russian landowners in the 1930s.
He said: "The comparison was about the philosophy and the Marxism.
"Nobody is suggesting that Jeremy Corbyn is going to line people up and shoot them, nobody is suggesting that."
