Boris Johnson is to meet the Irish prime minister for last-ditch Brexit talks on Thursday, after the EU’s chief negotiator publicly dismantled his proposals in a comprehensive point-by-point rebuttal.

With a make-or-break summit looming next week, high-level talks will also take place in Brussels between brexit secretary Steve Barclay and Michel Barnier – who warned on Wednesday that the two sides were “not really in a position where we’re able to find an agreement”.

Following claims from a Downing Street source earlier in the week that talks were on the verge of collapse, Mr Johnson will meet taoiseach Leo Varadkar privately in the northwest of England.

No 10 to says the meeting is necessarily for “both leaders and their teams to have detailed discussions” and find a way forward.

In a speech to the European parliament on Wednesday Michel Barnier listed three “serious concerns” with British plans: that they did not prevent a customs border, that they were not actually ready or “legally operable”, and that they could be unilaterally scrapped by Stormont and even never actually come into effect act all.

He said the proposals represented “a significant risk to the integrity of the single market” and warned: “Time is pressing. We are one week away form the European Council summit and just a few weeks away from the date of 31 October”.

Mr Barnier earlier briefed EU commissioners at a cabinet meeting in Brussels on the proposals. Gunther Oettinger, Germany’s EU commissioner, told reporters: “Once again, we discussed the proposal from the British government, and basically, all colleagues agreed with Barnier: namely the proposal from the British government does not represent a satisfactory solution.”

Later Mr Barnier told the European parliament: “Why are we not in a position to reach a deal yet? The British proposals have led to three serious concerns.

“What we’re being asked for in reality is to accept a system that hasn’t been properly developed, that hasn’t been tested: there will be controls spread out across Ireland and it will largely be based on exemptions and derogations on technology that is yet to be developed. Changes to international law through the common transit convention but with none of the guarantees that should be set out in this protocol,” he said.

“We need to have proper, rigorous checks all along the border of the single market. We need operational, real controls – credible controls. We’re talking about the credibility of the single market here to consumers, companies, and third countries that we negotiate agreements with.”

The second point raised by Mr Barnier was that the UK proposals are not “legally operational” – that the UK was in fact asking to come up with the answers to how to manage the border later in the transition period.

“By taking away that safety net, the backstop, and looking for alternative solutions later in the transition period, that British proposal does not give us that same security that we have in the backstop.”

Finally, Mr Barnier rejected the veto British plans would give to the Northern Ireland Assembly and executive, which would have to vote on them every four years.

“We are looking for a more important role for the Northern Irish institutions to ensure that the Good Friday or Belfast Agreement is respected,” he said.

“Unfortunately, the British proposals as it stands simply has the implementation of the protocol based on a unilateral decision on the Northern Irish authorities who could decide right from the very start – the day after the ratification – simply not to activate the proposed solution for Northern Ireland. Even if it were to be implemented, every four years they could call this into question.”

Speaking in the same debate, European parliament Brexit coordinator Guy Verhofstadt let rip at Brexiteers, who he branded “the real traitors” in response to rhetoric from Boris Johnson’s side that spoke of “surrender” by pro-EU British MPs.

“I will be less diplomatic than Michel Barnier. I think the proposal that Boris Johnson put forward exactly one week ago was not serious at all, dear colleagues,” he told MEPs.

“Not serious at all, because it was in fact – I call it a virtual proposal – not a real proposal. It gives a veto to the DUP, it puts customs facilities not on the border but in all the other parts of the islands of Ireland.”

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He also questioned why some Labour MPs had hinted they would vote for the plan, stating that UK moves to rip up environmental, social and labour standards “should be contrary to all the things Labour has defended in the past”.

European Commission president Jean-Claude Juncker had told French newspaper Les Echos overnight that the UK would “collapse” in the event of a no deal.

A spokesperson for the European Commission said in a statement after Wednesday’s meeting that the “EU remains constructive even when British emotions run high” – an apparent reference to hostile briefings emanating from Downing Street earlier in the week.