Boris Johnson has been told that he will have to fund his proposals for a bridge between Northern Ireland and Scotland.
The Irish prime minister did not dismiss the idea of such a bridge, but ruled out paying for it.
Last week Johnson revived his calls for the bridge describing it as a “very interesting idea”, adding: “Watch this space.”
Leo Varadkar said he had discussed the idea with the prime minister – claiming it was “worth examining”.
But the Taoiseach said he had also told Johnson he would expect the UK to pay for it.
“At which point he suggested, ‘no, no, the EU is going to pay for it’,” Varadkar said.
“So that’s definitely not going to happen, because neither Northern Ireland or Scotland are going to be in the EU. But it was kind of half serious, half joking in a way.
“But all messing aside, I do think at the very least a high-level engineering assessment should be done as to whether it is a viable proposal.”
Varadkar added: “I know people dismiss these things out of hand, but they used to dismiss the Channel Tunnel as well – the idea of building a tunnel between France and Britain – and I know what I see when I see a bridge tunnel between Denmark and Sweden, when you fly over New Orleans and you see 110 miles of bridge, it’s extraordinary,” he said.
“I think we need to at least check out is this viable in engineering terms and how much money it would cost to do.”
Johnson had previously claimed that the bridge proposals would cost £15 billion – but Johnson has been previously accused of understating costs involving bridges when he proposed the London Garden Bridge.
Last year a take down of the Irish bridge proposals by an engineer went viral after it was pointed out how impractical such plans would be.
James Duncan said that “no sane contractor or responsible government” would sanction the construction because of the complexity involved.
In a damning indictment of Johnson, he calls it a “thoughtless soundbite” that is “typical of Johnson”.