The Government has issued a fresh warning to Theresa May that the deadlock in the Brexit negotiations cannot be broken until it is clear there will be no ‘hard border’.
Arriving in Brussels for a gathering of leaders from the EU and former Soviet states, the British Prime Minister said it was time to move on to the "next stage" in the negotiations, including talks on a free trade deal.
However foreign affairs minister Simon Coveney insisted EU leaders would not give the green light for the phase two negotiations to begin at their summit in December unless there was progress on the border issue.
He said British assurances on the issue were "aspirational" and that there had to be a "credible roadmap" from the UK setting out how they would ensure there was no return to a hard border.
With the UK committed to withdrawing from customs union and the single market, Mr Coveney said it was difficult to see how they could avoid border checks if it resulted in "regulatory divergence" between north and south.
"We can't move to phase two on the basis of aspiration.
"We have move to phase two on the basis of a credible road map or the parameters around which we can design a credible road map to ensure that it doesn't happen," he said.
"The truth is that if we see regulatory divergence between the two jurisdictions on the island of Ireland it is very hard to see in that scenario how you avoid hard border checks. So we need progress on this issue in the context of the regulatory divergence issues.
"I hope and expect that we can get that by December so that we can all move on.
"If we can't, then I think there is going to be a difficulty coming up."
Mr Coveney added that the other member states were fully behind Ireland's stance on the issue.
"I don't think Ireland will have to block anything on its own. There is absolute solidarity across 27 countries here. They are with Ireland on this," he said.
"We are not talking about a 'no deal' here. What we are talking about is whether we can move on to opening up phase two in parallel with phase one issues in December.
"Without sufficient progress on the Irish issues that can't happen."
Mrs May said she hoped the EU and the UK would be able to "step forward" together into the second phase of the negotiations.
"These negotiations are continuing but what I am clear about is that we must step forward together," she said.
"This is for both the UK and the European Union to move onto the next stage."
The Prime Minister is due to hold one-to-one talks with European Council president Donald Tusk, after he warned last week that the phase two negotiations would not get the go ahead at the December summit unless there was further progress on the terms of Britain's withdrawal by the start of the month.
Since then the British Cabinet has met to discuss what it would be prepared to pay to settle the UK's "divorce bill" in order to end the stalemate.
Mr Tusk will be expected to probe her on reports that ministers agreed to double the sum originally put on the table by Mrs May to around £40 billion (€45 million).
However it is thought she does not want to name a precise figure until she has a clear idea of what kind of trade deal is available with the remaining EU member states in the phase two negotiations.