The European parliament has told Boris Johnson that his proposals for the Irish border do not “even remotely” amount to an acceptable deal for the EU, in comments echoed by Ireland’s prime minister.

The committee of MEPs representing the parliament’s views on Brexit said the prime minister’s proposals could not form the basis for an agreement, describing them as a “last-minute” effort. The European parliament will have a veto on any withdrawal agreement.

“Safeguarding peace and stability on the island of Ireland, protection of citizens and EU’s legal order has to be the main focus of any deal,” it said in a statement. “The UK proposals do not match even remotely what was agreed as a sufficient compromise in the backstop.”

Ireland’s prime minister, Leo Varadkar, also accused Johnson of contradicting his own proposals during an appearance by the British prime minister in the Commons, in which he sought to convince MPs there would be no return of a hard Irish border.

Speaking shortly after Johnson addressed the Commons, Varadkar highlighted a discrepancy between Johnson’s words and the legal text tabled by the UK government.

“I am reassured by what Prime Minister Johnson said today: that he is not proposing that there should be any new physical infrastructure on the island of Ireland linked to customs or customs checks,” Varadkar said.

“But that is actually in contradiction to the papers presented by the UK government yesterday. So I think working with the EU taskforce in part, [Michel] Barnier’s taskforce, and also talking with the UK government we will have to tease out the detail of what those proposals mean.”

In a barbed comment, Varadkar further suggested the British public had changed its mind on Brexit but was being prevented from having its voice heard. “All the polls since Mr Johnson became PM suggest that’s what the British people actually want, but their political system is not able to give them that choice,” he said.

Guy Verhofstadt, the former prime minister of Belgium who coordinates the European parliament’s Brexit steering group, said it was “nearly impossible” to see how a deal could be secured on the basis of the proposals.

He pointed to a leaked script handed to Conservative MPs by the party, which instructed them to attack the EU as “crazy” if it rejected proposals as an indication of Johnson’s insincerity about wanting a deal.

“If there is a Tory document saying that they have to blame the European Union then it’s obvious that that is the purpose,” he said.

The prime minister had said in his letter to the European commission president, Jean-Claude Juncker, accompanying the legal text of the UK’s proposals for replacing the Irish backstop that his ideas amounted to a “broad landing zone” for a deal.

He will now be tested by the EU on how far he will compromise on the key areas of contention, in particular on the imposition of a customs border on the island of Ireland, a seeming red line for the new government.

The parliament’s Brexit steering group said the plan for customs checks and controls on the island of Ireland would “breach a range of fundamental principles and red lines”.

“The UK proposals on customs and on regulatory aspects explicitly provide for infrastructure, controls and checks but are unclear as to exactly where and how these would be carried out,” the committee said. “Any form of controls and checks in and around the border would signify the end of frictionless trade and as such would harm the all-island economy as well as represent a serious risk to the peace process, and could imply a serious risk for our consumers and businesses.”

The MEPs said the parliament would also veto any withdrawal agreement that did not provide a failsafe solution for avoiding a hard border on the island of Ireland.

The UK’s suggestion of working out the details of how technology could be used to help with that during the Brexit transition period was said to be unacceptable.

Johnson has proposed that Northern Ireland stay in the EU’s single market for goods on the basis that Stormont agrees in a vote before the end of the transition period, and then every four years.

The committee said this provided a unilateral right to exit arrangements that would create huge uncertainty for the Republic of Ireland.

The MEPs said: “The right of consent being offered to the Northern Irish assembly effectively makes an agreement contingent, uncertain, provisional, unilateral, instead of the safety net provided for by the backstop.

“Furthermore, the Northern Irish assembly has not sat for nearly three years, and it is questionable whether it would be able to reconvene and take on the responsibility for an international treaty of this nature.”

The UK’s negotiator, David Frost, is expected back in Brussels on Friday, possibly with the Brexit secretary, Stephen Barclay. EU sources said that it was crucial for him to indicate that the government was willing to give further ground to get a deal before 31 October when the UK is due to leave the bloc.

A European commission spokeswoman said it was up the British government to move its position for progress to be possible, and that Juncker had made that point in a phone call with Johnson.

She said: “There are problematic points in the UK’s proposal and further work is needed. This work is for the UK to do, not the other way around.”

Speaking after a meeting with Sweden’s prime minister, Varadkar said Ireland’s objective remained to avoid “any customs posts between north and south or any tariffs or restraints on trade between north and south”.

“They were all abolished in the 1990s,” Varadkar said. “We don’t want to go back to that. The majority of the people in the north don’t, the majority of the people in the Republic of Ireland don’t. But if we are going to be in two customs unions that is going to be incredibly hard to reconcile.”

Speaking to MPs in the Commons earlier in the day, Johnson insisted that the whole of the UK would leave the EU’s customs union on 31 October and that this was a fundamental part of his vision for the country.

Asked by the former cabinet minister Damian Green whether this would involve extra infrastructure anywhere on the island of Ireland, Johnson reassured him that it would not. “I can tell him that absolutely not. The proposals we are putting forward do not involve physical infrastructure at or near the border or indeed at any other place.”

But an explanatory document tabled with the European commission appears to suggest there would be both a need to police the area to avoid smuggling and that customs checks would be carried out “at traders’ premises or other designated locations which could be located anywhere in Ireland or Northern Ireland”.