German Chancellor Angela Merkel told the Taoiseach a hard border has to be on the table in a no-deal Brexit scenario, it has emerged.
Europe’s longest-serving leader questioned Leo Varadkar’s hard-line stance on the Border amid fears it was undercutting the EU’s negotiating position.
The Irish Government has repeatedly insisted it is not preparing to erect any physical infrastructure at the Border, even if the UK crashes out without a deal on March 29.
But during a 40-minute phone call in early January, Ms Merkel suggested this approach was giving ammunition to Brexiteers in London.
Opponents of the so-called backstop, which ties Northern Ireland to EU regulations unless and until a workable trade deal is agreed, claim it is unnecessary because both he UK and Ireland have said they will not erect a border.
According to Bloomberg, Mr Varadkar explained to Ms Merkel that no Irish government would accept checkpoints that could become targets for violence.
Sources last night confirmed the accuracy of the report, but noted that Mr Varadkar has acknowledged “the only way to avoid a border in the long-term is to have customs and regulatory alignment”.
Since the phone call, Ms Merkel has publicly defended the need for the backstop. Meanwhile, both the Taoiseach and Fianna Fáil leader have insisted EU solidarity on the backstop is watertight.
The phone call between Mr Vardakar and Ms Merkel has been described by officials in Dublin as a “brainstorming session” during which he explained the context of the Irish situation.
Earlier this week, Ms Merkel said the EU and UK "must do everything to achieve an orderly Brexit" but a deal "must be a fair agreement that works in practice and we have some work ahead".
It comes as pro-Brexit members of Theresa May's government were reported as saying they are willing to accept a five-year limit on the backstop - a proposal that has already been rejected by the EU.
Speaking at the All-Island Civic Dialogue on Brexit, Mr Varadkar said: "Ireland's concerns on the Border have become EU concerns. Our insistence on a legally binding and operable means to avoid a hard Border has become an EU insistence."
The Taoiseach said those predicting the EU will abandon Ireland at the last minute in order to secure a Brexit deal "are in for a nasty surprise".
Fianna Fáil leader Micheál Martin said: "There is no scenario where they [the EU27] will force Ireland to accept a deal." However, what happens if the UK leaves without a deal is less clear. The Border will become an EU frontier which Ireland will be expected to police in order to protect the single market.
The official Irish position now is that in a no-deal scenario "difficult discussions" between the UK, Ireland and EU will have to take place.
Tánaiste Simon Coveney indicated yesterday that Ireland will argue the UK must live up to its promise of avoiding a hard border through regulatory alignment even if it crashes out.
The Government has rejected suggestions from unnamed EU diplomats that an alternative to a hard border on the island would be for checks on goods leaving Ireland for the continent.
Mr Coveney said he is "suspicious" of such ideas coming from anonymous sources who may have an agenda.
However, they echo comments made in recent weeks by Belgium MEP Philippe Lamberts, a member of the Brexit steering group of the European Parliament.
"If Ireland refuses to protect the Border with Northern Ireland after a hard Brexit, we would have to relocate the customs border to the continent," he told German news outlet 'Der Spiegel'.
Mr Varadkar sought to categorically deny this proposal yesterday, saying: "We are founder members of the single market. We can't allow a decision made in Britain to leave the European Union to undermine our membership of the single market and customs union, which we will protect."
He added that checks on goods leaving Ireland "would create a hard border between Ireland and the European Union and that is not something we can accept".
Meanwhile, in a rare public appearance, former Taoiseach Brian Cowen has described the position of the UK parliament on Brexit as "unreasonable".
Addressing a meeting in Belfast, Mr Cowen said it is "a great failure in the negotiating process generally - not attributing any blame to anybody - that we have to come to this point where we don't have the clarity that one would expect after two years of arduous negotiation".
Mrs May did received a boost last night when US President Donald Trump predicted trade between the US and UK will increase "very substantially" after Brexit. "We're agreeing to go forward and preserve our trade agreement.
"You know all of the situation with respect to Brexit and the complexity and the problems, but we have a very good trading relationship with the UK and that's just been strengthened further.
"So with the UK we're continuing our trade and we're going to actually be increasing it very substantially as time goes by," Mr Trump said.