Ireland will have to protect its place in the single market should the UK leave the EU without a deal, the country’s deputy prime minister says.
Simon Coveney told the BBC the decision to have a no-deal Brexit would be the UK’s but added everybody would lose.
Checks “of some sorts” would have to be carried out in Ireland, he said.
Mr Coveney warned if the new UK prime minister’s approach was to “tear up” the existing withdrawal agreement with the EU, then “we’re in trouble”.
“That’s a little bit like saying, ‘Give me what I want or I’m going to burn the house down for everybody,'” he told the BBC’s Andrew Marr Show.
He said he hoped the UK and EU would negotiate a future relationship that would mean the so-called backstop – designed as an insurance policy to prevent a hard border on the island of Ireland – could be avoided.
However, he warned it could not be removed from the withdrawal agreement.
“The EU has made it very clear that we want to engage with the new British prime minister, we want to avoid a no-deal Brexit but the solutions that have been put in place to do that haven’t changed,” Mr Coveney said.
“If the British government forces a no-deal Brexit on everybody else, the Republic of Ireland will have no choice but to protect its own place in the EU single market. That would fundamentally disrupt the all-Ireland economy.”
He said the all-Ireland economy had helped maintain peace on the island of Ireland but that protecting it would “not be possible” in the event of a no-deal Brexit.
However, he added that contingency plans were being drawn up with the European Commission to try to minimise the disruption.
The withdrawal agreement has been rejected three times by MPs in the Commons, with the backstop a key sticking point among Brexiteers.
The two men vying to become the next prime minister, Boris Johnson and Jeremy Hunt, have said the backstop is “dead” – a position seen as increasing the likelihood of a no-deal Brexit.
If MPs fail to support a Brexit deal agreed between UK and EU by 31 October, the legal default is to leave with no deal on that date.
Both contenders to be the next prime minister have said they want to leave on that date and renegotiate with the EU, leaving with a deal.
But Mr Hunt and Mr Johnson have also said they would keep the possibility of no deal on the table to strengthen negotiations, despite Parliament voting to rule the option out.
Mr Johnson has also refused to rule out suspending Parliament to force a no-deal Brexit through.
This week, MPs backed a bid to make it harder for a new prime minister to do this.
A majority of 41 approved the amendment, with four cabinet ministers, including Chancellor Philip Hammond, abstaining.