Ireland has called on the UK to abandon moves to unpick parts of its Brexit treaty, warning that London risks forfeiting the EU’s trust as time runs out in talks on a free trade deal.

Micheál Martin, the Irish premier, said Prime Minister Boris Johnson’s decision to table a controversial new bill that would modify those parts of the EU withdrawal agreement relating to Northern Ireland raised “justifiable doubts” as to whether the UK wanted to conclude trade negotiations.

“I think the British government needs to move to restore trust and to give meaningful reassurance to the European negotiators,” Mr Martin told the Financial Times.

“Our colleagues in Europe, in particular those conducting the negotiations, are now wondering whether the will is there or not to arrive at a conclusion and get an agreement — and that is a very serious issue.”

He joined a chorus of critics targeting Mr Johnson. The European Commission said in an internal analysis paper on Wednesday that the UK plans amounted to a “clear breach” of the Brexit treaty.

Mr Martin said the sections of Mr Johnson’s internal market bill that would undermine the agreement “should be withdrawn”. 

“In my view, the sensible thing would be to withdraw those clauses, but it's a matter for the British government now to decide how it is going to engage with the EU negotiators in how it seeks to restore trust and credibility to the process,” he said. 

Mr Martin held a 30-minute phone call with Mr Johnson on Wednesday in which he set out in “forthright terms” his “very strong concerns” about plans to overwrite parts of the Brexit treaty. The bill, he said, “essentially nullifies and undermines what is an international treaty”. 

Mr Martin, who said he had a good meeting in August with Mr Johnson at which they agreed to “work closely together”, complained that he had no prior notice of the move. “This is no way to behave in terms of international relations in my view. I pointed out we had no heads-up.” 

He also complained that the UK move was bad for Northern Ireland. “It’s potentially divisive in terms of the politics of Northern Ireland and from that perspective is most unwelcome,” he said. 

Mr Martin’s intervention, ahead of a special meeting of the EU-UK joint committee that oversees how the withdrawal treaty operates on Thursday, reflects anger in Dublin, Brussels and other EU capitals at the moves to recast key provisions to maintain open borders in Ireland. 

According to the taoiseach, Mr Johnson told him the UK was “absolutely committed” to fulfilling its obligations on Irish trade issues. However, Mr Martin said the Westminster bill “runs counter” to that assertion. 

“Put it this way: I think he fully understands where I am coming from and where the Irish government is coming from and I think he understands the issues,” he said. 

“Clearly the EU are not happy about this. They are taking this very seriously and they want to hear an account from the British side as to what this is all about.”

Mr Martin dismissed Downing Street claims that Mr Johnson did not fully understand what he had agreed in the withdrawal treaty and he disputed the prime minister’s assertion that the Westminster bill was in Northern Ireland’s interests. 

“This deal was presented to the British public as oven-ready . . . It’s difficult to comprehend that people did not know or were not aware of the implications of the withdrawal treaty and indeed the Northern Ireland protocol,” he said.

“I don’t accept at all that this is somehow preserving the Northern Ireland peace process. What has happened today in my view is damaging to the politics of Northern Ireland.” 

Mr Martin added: “We accept there [are] different views on Brexit in the north. Different parties have different views, but nonetheless there was an acceptance of the de facto reality of the protocol and the withdrawal agreement.” 

Before taking power in June at the helm of a three-party coalition, as opposition leader Mr Martin supported both the withdrawal agreement and the previous Irish government’s push to maintain frictionless borders. 

To keep the frontier open — and thus protect the 1998 Good Friday peace pact that ended decades of political violence in Northern Ireland — the treaty binds the region to the EU’s customs and trade regime at the end of the transition period on December 31, unlike the rest of the UK.

But the bill presented to the parliament at Westminster on Wednesday would give Britain sweeping powers to overwrite sections of the agreement agreed with Brussels last year, even if this led to “inconsistency or incompatibility” with international and domestic law.

Mr Martin insisted a trade deal was still possible, saying a “landing zone” was in sight. However, he added: “Time is running out and I think bona fides have to be established here in terms of a genuine will to get a sensible agreement.

“Above all, a no deal would be very damaging to all concerned and there is an obligation on us, on all leaders, to act responsibly in terms of protecting people’s livelihoods and their jobs and that’s what it’s about now.”