EU leaders will want to see who emerges as British prime minister from the Conservative party’s leadership contest before considering an extension of the negotiating time allowed under article 50.

A special summit could be held in January to assess the situation, EU diplomats said, but agreement on a prolongation beyond 29 March 2019 would be far from certain.

In her response to the vote of confidence in her leadership, Theresa May had claimed on the steps of Downing Street that whoever took her job would have to scrap or extend article 50, the mechanism taking Britain out of the EU on 29 March, “delaying or even stopping Brexit”.

Brussels has repeatedly warned it would not countenance an extension of the two-year negotiating period to simply allow a “managed no-deal”, which would likely be the preferred way forward by some candidates for May’s job.

It has been reported that the foreign secretary, Jeremy Hunt, and the home secretary, Sajid Javid, could champion a withdrawal on such terms.

There would also be doubts among the 27 EU member states about the wisdom of granting an extension should Boris Johnson end up in Downing Street, given what the EU regards as his unrealistic aspirations for the talks.

Sources said that while there would be no “ideological” objection to an extension there would be a clear interest among the EU’s leaders to know what the purpose would be of extra-time.

“Prolongation is not probable and not realistic because then you’d need a new summit in January to create unity on our side”, one diplomat said.

Reacting to the developments in London, diplomats for the 27 said they were not surprised by the leadership challenge but warned that the “difficult mess” in Westminster had increased the risk of the UK leaving without a deal.

“Now is a much more difficult position,” an EU diplomat said, “as nobody knows anything. May has no idea what will be her life after 6pm”.

European politicians were loth to worsen the situation for May, whose tenacity is at least respected, by commenting on the challenge to her premiership.

The Dutch prime minister, Mark Rutte, who saw May in The Hague on Tuesday, said: “I am very fond of my British colleague, but I never say anything about voting in other countries.”

A spokesman for the European commission said: “The commission won’t comment on internal politics of UK, let alone on the internal processes of the Conservative party, but President Junker has many times expressed his support for PM May and her role in managing this difficult process”.

After Rutte, May had visited the German chancellor, Angela Merkel, in Berlin and Donald Tusk, the European council president, and Jean-Claude Juncker in Brussels, as she sought to secure help in getting her deal through parliament.

EU diplomats have not discussed the nature of the help that could be offered. One senior diplomat said it was “not realistic” to expect a text before Christmas, while voicing unhappiness that Tusk had announced a last-minute Brexit meeting at Thursday’s EU summit without consulting national capitals.

The diplomat added that it was not Tusk’s fault, because of the difficult situation in the UK. “London is a mess, everything is horrible,” they said.

“The nervous atmosphere gets tenser and tenser. Hopes are still there but joy is zero. It is now below anything that I ever expected, it is not even a process based on any kind of predictability,” the source said.

“It’s getting so messy and absurd that even the funny elements of this are actually tragic … in this muddy soupy kind of drama we can also see these days it is difficult to get any sense of meaning or orientation, but I still can’t be so undiplomatic to tell you that there is no hope.”

Asked whether the UK had the most unstable government in Europe, the source replied: “Is there a government in London actually?”

The EU is stepping up its no-deal preparations and member states are calling on the European commission to publish legal acts from January to help avoid the messy consequences if the UK leaves without a withdrawal agreement.

