Boris Johnson would have been acting in "bad faith" by pressing ahead with proposals for a string of checks on both sides of the border, the Taoiseach has said.
Welcoming the fact that Mr Johnson appears to have "disowned and distanced" himself from reports that the UK would replace the backstop with customs infrastructure between five and 10 miles away from the border, Leo Varadkar said: "Had he not, in my view, it would have been hard evidence of bad faith on behalf of the British Government."
Mr Varadkar added that the Irish Government expects the UK to honour the agreement that there will be no hard border post Brexit.
"No British Government should try to impose a solution upon Ireland which is opposed by the people of Ireland, north and south," Mr Varadkar told the Dáil.
However, he admitted that if Britain crashes out of the EU at the end of the month checks will be required at ports, airports, at business level and near the border.
Asked about the reports claiming the UK's so-called 'non-papers' had included details of customs clearance posts on both sides of the border, Mr Johnson said: "They are not talking about the proposals we are going to be tabling, they are talking about stuff that went in previously.
"But clearly this is the moment when the rubber hits the road.
The Taoiseach said it was clear from speaking to Mr Johnson in New York last week, that the UK including Northern Ireland is intent on leaving the customs union.
However, he indicated that Mr Johnson perhaps did not understand that all other options to replace the backstop had been ruled out during lengthy talks between the UK and EU.
He said both sides had been "going up and down all these rabbit holes" during two years of negotiations under former British prime minister Theresa May.
"I explained to him when we met in New York, there is a reason we came up with the deal we did after two years of negotiations with prime minister May and her Government," Mr Varadkar told the Dáil.
"Very often those who were not part of negotiating an agreement do not know why those negotiations reached a certain point, but this is why we reached that point."
Pressed by Fianna Fáil leader, Micheál Martin, Mr Varadkar said the Irish Government had not seen the 'non-papers' but said he was aware of their existence as this had been in the public domain.
Later in the day, Mr Varadkar told TDs that there are a number of options available to avoid a hard border, some of which would not be considered.
These include a united Ireland; Britain remaining in the EU or Britain remaining in the single market and customs union.
He also knocked back the possibility of Ireland joining the UK: "I do not think anyone in this House would entertain that option."