THE "moment of truth" in the Brexit negotiations is fast approaching, Michel Barnier has claimed, making clear the European Union is still hoping for agreement on so-called withdrawal issues "in the next few days".

As the clock ticks down to a crunch dinner on December 4 between Theresa May and Jean-Claude Juncker, the European Commission President, the EU’s chief negotiator called for "real, sufficient progress" on the Brexit "divorce bill", citizens' rights and the Irish border, so that EU leaders could give the green light to talks beginning on trade and transition before Christmas.

At an EU summit in Tallinn, Mr Barnier said: "The moment of truth is approaching; we have a council under the Estonian presidency on December 14 and 15 and I really hope that will be the point where we will see real, sufficient progress on the conditions of our separation.

"And that will allow me to recommend the opening up of the next two phases of negotiations, first of all on the transition period and then on the future relationship."

This appears to be the first time the EU negotiator has indicted three rather than two phases to the Brexit talks.

He spoke as the Irish border continued to appear to be the main stumbling block to achieving “sufficient progress” as Simon Coveney, Ireland's Foreign Minister, made clear that all EU27 leaders agreed that trade talks could not start unless Britain offered further assurances that there would be no hard border with Northern Ireland.

He said Ireland would not need to use its veto to prevent progress in talks because EU negotiators would block it themselves if the UK did not offer a workable solution on the Irish border.

He claimed last week he received personal assurances from Mr Juncker, Mr Barnier, and Donald Tusk, the European Council President, that Brussels would hold firm on this demand.

"They have repeated the message that Ireland's problems are the EU's problem, so Ireland is not going to be isolated and forced to use a veto," declared Mr Coveney.

EU leaders insist a hardening of the border is inevitable if the UK were to leave the single market and customs union as checks would be required to monitor movement between jurisdictions operating under two different regulatory systems.

One solution offered by Europe is the suggestion Northern Ireland would continue to comply with EU regulations post-Brexit but this has been firmly rejected by the UK Government.

Any arrangement which appeared to give Northern Ireland a separate status would also be strongly resisted by the Democratic Unionists, whose 10 MPs are effectively keeping the Prime Minister in Downing Street after she lost her majority at the General Election.

Asked about the prospect of movement on the border issue, Mrs May’s spokesman said Britain was "firmly committed" to avoiding a physical frontier.

He confirmed that Liam Fox, the International Trade Secretary, at the weekend by suggesting that the border issue could not be resolved in the first phase of talks because it had to form part of the second phase on trade was confirming the UK Government’s policy.

"In order to be able to see what the solution is going to finally look like, we need to understand what the future trading relationship is going to be, because the two things are obviously related. We want to get on to talking about trade as soon as possible," said the spokesman.

Meanwhile, Neale Richmond, an Irish senator, who is a European affairs minister for the ruling Fine Gael party, warned of violence if there were a return to a hard border. He said: “You put up one watchtower or put out one customs patrol and they will be a target. I would argue they would be attacked within a week of them going up.”

In Dublin, Leo Varadkar, the Taoiseach, was holding talks with Micheal Martin of Fianna Fail in a bid to avert a vote of no confidence in his government due Tuesday, which, if passed, could spark a snap General Election in Ireland.