EU officials are ready to look at “realistic” proposals from Boris Johnson on the Irish backstop – the main obstacle to a Brexit deal – but are pessimistic about his government’s chances of coming up with workable ideas.

Downing Street’s optimism over an apparent shift in the EU’s willingness to negotiate could be scuppered by a new Irish push to reinforce the importance of the insurance policy against a hard border on the island of Ireland.

Johnson’s Europe envoy, David Frost, is due to return to Brussels on Wednesday for meetings with officials as both sides strive to avoid a no-deal Brexit on 31 October.

Brexit: No 10 optimistic over EU 'shift' but Ireland presses for backstop Read more

After the G7 summit and meetings with Angela Merkel and Emmanuel Macron in Berlin and Paris, the EU is taking the prime minister more seriously as a dealmaker. EU officials now think he is genuine about wanting an agreement, but are sceptical he can bring his party with him.

One senior EU official told the Guardian the sequence of meetings in Berlin, Paris and Biarritz had introduced a new dynamic: “While we are not in a situation where we are thinking that Johnson is really serious about a deal, at least there is that possibility that he might be and that is a big change.”

“The political arithmetic hasn’t changed, the political timetable hasn’t changed. But we have to listen and we have to look [at his ideas],” the official added.

Johnson spoke to the president of the European commission, Jean-Claude Juncker, on Tuesday evening. A commission statement said that in the call “President Juncker repeated his willingness to work constructively with prime minister Johnson and to look at any concrete proposals he may have, as long as they are compatible with the withdrawal agreement. A ‘no-deal’ scenario will only ever be the UK’s decision, not the EU’s.”

A Downing Street source said that there was still not a substantive “openness to action” despite a “shift in rhetoric” from EU leaders. No 10 believes the EU27 must consider whether to approve a new negotiating mandate, something hinted at by Juncker in his call with Johnson. “That would be a sign they are serious about this,” a source said.

The EU sees a chance to reach a deal after Johnson declared in Berlin last week that he was more than happy to accept a “blistering timetable” of 30 days to find a compromise. This U-turn from his previous refusal to talk unless the EU scrapped the backstop was seen as an important shift in the UK accepting the onus of finding the solution.

Quick guide What is the Brexit ‘backstop’? Show Hide What is the original ‘backstop’ in the withdrawal agreement? Variously described as an insurance policy or safety net, the backstop is a device in the withdrawal agreement intended to ensure that there will not be a hard border between Northern Ireland and the Republic of Ireland, even if no formal deal can be reached on trade and security arrangements. It would mean that if there were no workable agreement on such matters, Northern Ireland would stay in the customs union and much of the single market, guaranteeing a friction-free border with the Republic. This would keep the Good Friday agreement intact. Both the UK and EU signed up to the basic idea in December 2017 as part of the initial Brexit deal, but there have been disagreements since on how it would work. The DUP have objected to it, as it potentially treats Northern Ireland differently from the rest of the UK, creating a customs divide in the Irish Sea, which is anathema to the unionist party. Hardline Tory Eurosceptics also object to it, as they perceive it to be a trap that could potentially lock the UK into the EU’s customs union permanently if the UK & EU cannot seal a free trade agreement. That would prevent the UK from doing its own free trade deals with nations outside the bloc. What was added to May’s withdrawal agreement? Joint interpretative instrument

A legal add-on to the withdrawal agreement was given to Theresa May in January 2019 to try to get her deal through the UK parliament. It gives legal force to a letter from Jean-Claude Juncker and Donald Tusk, the presidents of the commission and council. This stated the EU’s intention to negotiate an alternative to the backstop so it would not be triggered, or, if it was triggered, to get out of it as quickly as possible. Unilateral statement from the UK This set out the British position that, if the backstop were to become permanent and talks on an alternative were going nowhere, the UK believes it would be able to exit the arrangement. Additional language in political declaration This emphasises the urgency felt on both sides to negotiate an alternative to the backstop, and flesh out what a technological fix would look like. However, it failed to persuade the attorney general, Geoffrey Cox, who said that while it ‘reduces the risk’ of the UK being trapped in a backstop indefinitely, it does not remove it. What happens next? Boris Johnson declared the Northern Ireland backstop ‘dead’ during his leadership campaign, and promised to throw it out of any deal he renegotiated with the EU. The EU has repeatedly stated that it will not reopen the withdrawal agreement for renegotiation. Daniel Boffey, Martin Belam and Peter Walker

“The ball is in London’s court,” said an EU diplomat. “Boris Johnson hasn’t tabled a concrete plan, but there is certainly a slight hope that a solution can be found.”

It is understood No 10 believes there has been a “rhetorical shift” from the EU compared with a month ago when the backstop and withdrawal agreement were considered sacrosanct.

This subtle change has been signalled by the EU chief negotiator, Michel Barnier, who said the bloc was ready to analyse British proposals that were “realistic, operational and compatible with our principles”.

Diplomats have pointed out that the backstop is written as a protocol, separate to the withdrawal agreement. Although this interpretation is not shared by all Brussels insiders, such nuances could open the way to a face-saving compromise.

Legal niceties aside, all EU officials stress that any alternative to the backstop must do the same job. “A withdrawal agreement … without having an insurance policy is not going to work,” said another EU diplomat. “We are quite serious about looking at proposals from the UK side to do it differently.”

The diplomat said they were “not optimistic” Johnson could deliver. “We haven’t seen anything from the UK yet that gives an indication of where they want to go and therefore there is nothing we can entertain.”

Johnson is expected to meet Ireland’s taoiseach, Leo Varadkar, in Dublin early next week, a meeting that a Downing Street source described as “clearly crucial”.

Ireland’s deputy prime minister, Simon Coveney, started a five-city Brexit tour of EU capitals on Tuesday to reinforce the importance of the backstop and Good Friday agreement for Ireland’s economic and social stability, in a challenge to the perception that the EU is showing signs of flexibility on the measure.

In an indication that no real breakthrough had been made at the G7 meeting in Biarritz, Coveney said on Tuesday during a visit to Prague that the alternative arrangements proposed in the UK did not come “close” to the guarantees needed and provided for by the backstop.

“I think we need to be honest here, that the alternative arrangements that have been discussed to date, do not do the same job as the backstop – not even close. And so let’s not pretend that solutions exist when they might not,” he said.

Facebook Twitter Pinterest Simon Coveney addresses the media in Prague on Tuesday. Photograph: Petr David Josek/AP

The narrow landing ground for a deal was illustrated by the cool reaction in Brussels to an alternative backstop plan drafted by a British former commission official and two academics. Jonathan Faull, who led the commission taskforce during David Cameron’s renegotiation, and his colleagues said they had come up with “an offer the EU and UK cannot refuse”.

The plan would allow different regulatory standards in Northern Ireland and Ireland while avoiding the need for a sea border. It would require the UK and Ireland to make it a criminal offence to knowingly export goods across the frontier that breached standards on either side. The proposal has attracted “considerable interest”, the authors told Politico.

But the senior EU official said it was a retread of Theresa May’s doomed Chequers plan, rejected by Brussels partly because it required the EU to outsource customs controls to the UK. “It is magical thinking written in very polite and crisp English,” the source said.

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Even if Johnson comes up with proposals that have eluded the British government for the last three years, he may have run out of time to pass them through parliament, where he has a majority of one.

EU insiders are also unconvinced that Johnson’s advisers or the Conservative party would support a compromise. “Is no deal better to secure his [Johnson’s] own position?” asked one diplomat. “Yes, because anything else will lead to the breakup of the Tory party. I do not see this Tory government going for a deal. That is what troubles me.”

A UK government spokesperson said: “We are ready to negotiate in good faith an alternative to the backstop with provisions to ensure the Irish border issues are dealt with where they should always have been: in the negotiations on the future agreement between the UK and the EU.

“The UK government is working at pace to find a wide range of flexible and creative solutions to the unique circumstances on the island of Ireland.”