The UK will not be saved from crashing out of the EU via an extension of the article 50 negotiations unless there is a major realignment in British politics, most likely through a second referendum or general election, senior diplomats and European commission officials have disclosed.

Among those calling for Theresa May to be ready to ask for a prolongation of the UK’s membership beyond 29 March 2019 should a no-deal scenario appear likely are the Commons’ exiting the EU select committee, chaired by Hilary Benn, and the former deputy prime minister Nick Clegg.

Yet EU sources insist that while Michel Barnier, the bloc’s chief negotiator, has repeatedly warned that the “clock is ticking”, including during his appearances in Brussels last week, it is not a lack of time that stands in the way of a deal being struck.

EU officials and diplomats have told the Guardian it would instead require a fundamental shift in British politics for there to be any value for the EU in an extension of the UK’s membership. That position is echoed in Berlin and Paris, among other EU capitals.

Article 50 can only be extended by the unanimous agreement of the 27 other member states, and on the request of the withdrawing state, which May has already said she is not prepared to do.

On Friday, Barnier picked apart the UK’s white paper, complaining that it would leave the EU open to fraud and burden European businesses with extra bureaucracy.

Play Video 1:01 Michel Barnier raises concerns over UK's latest Brexit plan – video

He told reporters he had offered to hold intensive talks with the new Brexit secretary, Dominic Raab, to find a solution to the problem of avoiding a hard border on the island of Ireland, without which there will not be a withdrawal agreement.

The Guardian understands that during a meeting of EU ministers with Barnier on Friday, astonishment was expressed at May’s comments in Belfast earlier in the day in which she accused the EU of seeking to constitutionally and economically “dislocate” the UK.

“We want to de-dramatise this, talk it all down, and so there was surprise at the aggressive tone,” one diplomat said. “It just gives her even less room for manoeuvre. If she wants to give up, she should just say so.”

But while the negotiations have rarely looked so in danger of failing, senior EU officials and diplomats do not see any purpose in an extension to article 50, the two-year negotiating period set aside for a member withdrawing from the union, unless there is a change in British politics that can offer genuine hope of a better outcome.

“If it is time just for the sake of putting off an inevitable no deal, then it will not happen,” one senior diplomat involved in the negotiations said.

Charles Grant, the director of the Centre for European Reform thinktank, said that following his discussions with French government officials and the commission it was clear that a high bar would be set for an extension.

“If there is a very good reason for it, then fine,” he said. “But if it is just because a deal hasn’t been agreed, then that’s not going to be fine. The commission and the French government say they are relaxed about a no deal, although I am not sure they are.”

The issue had yet to be formally discussed among those involved in the EU-UK negotiations, but informal discussions suggest there is limited appetite for such a development, sources in Brussels added.

“You have 27 member states who have to agree to it and I can’t see them all doing so. There will always be someone who is awkward, and wants something out of it. Spain might want to make a point about Gibraltar, for example,” said one diplomat involved in the Brexit negotiations.

“We have spent the GDP of Greece in terms of manpower in trying to first of all keep the Brits in and now negotiate on their exit. Even if the UK asked for it, and that seems unlikely, it would need a compelling reason to be given.”

Mujtaba Rahman, a former Treasury and European commission official, and now head of Europe for the Eurasia Group risk consultancy, said: “An extension can’t be an end in itself. It would need to come with political change in Westminster, a referendum, change of leader or general election, otherwise negotiations would risk remaining deadlocked. That’s the view of the commission, the European council, Berlin and Paris.”

Rahman said the European parliament would be opposed to an extension as it would play well for European populists, including Ukip, who could point to the failure of the political classes to respect the 2016 referendum result.

Officials in the parliament have taken legal advice, which suggests that extending article 50 beyond the next European elections in May would not only give 73 British MEPs a right to sit in the chamber until the UK leaves but for the full five-year term.

A source in the parliament said: “This has been repeatedly discussed. It would be the perfect opportunity for Ukip to rebuild, which is what no one wants. After all, Guy Verhofstadt [the parliament’s Brexit coordinator] has said before that the only good thing about Brexit is that Nigel Farage won’t be coming to Brussels again. The parliament won’t want them back again”.

Asked about the possibility of an extension of article 50, a senior British cabinet source said there had been no conversations within the government on the topic. He added that ministers were aware that such a request would likely prompt a collective “cardiac arrest” among leaders of member states.