Brussels is preparing to offer Boris Johnson a no-deal Brexit extension beyond 31 October in an attempt to help him keep the Conservative party together and provide one more chance to strike an agreement deal.

The extra period of EU membership would be used for renegotiation but could be billed to Conservative Brexiters as an opportunity to prepare further for leaving without a deal.

“It will be described as a technical delay to save Boris from political embarrassment but then we will have time to find an agreement,” said one senior EU diplomat.

There is growing confidence among key member states that a no-deal Brexit can be avoided after the Commons voted this week to prevent the next prime minister, likely to be Johnson, from proroguing parliament.

The details of the approach shared with the Guardian will aggravate hard Brexiters in Westminster who will see it as a serious threat to their expectations that the UK should depart on 31 October at any cost.

Under the proposal discussed in Brussels, Johnson could maintain that he is on course to leave without an agreement while keeping open the option of coming to a deal with the bloc.

EU leaders are also considering the steps they would take to avoid a crisis in the event that Johnson does press ahead with no deal on 31 October. A declaration has been mooted expressing the EU27’s regret at the lack of a deal and offering to re-engage if the UK accepts its financial commitments.

“How do we build back out of the abyss in a time where minds on both sides of the channel are probably not very consolatory?” a second diplomat said. “We need to pre-empt that moment and create a platform for re-engagement on the day the UK leaves which might be used once the dust has settled. Provided of course the existing obligations are settled.”

If Johnson is elected as Conservative leader next Tuesday and becomes prime minister, he is expected to visit key EU capitals in early August. A G7 meeting in Biarritz at the end of next month is regarded as an important stepping stone to finding a mutually advantageous way forward. An emergency Brexit summit could be held in September.

But the events this week have left key EU diplomats and officials convinced that no deal is now significantly less likely.

Philip Hammond signalled in an interview on Friday that he was prepared to vote to bring down a Johnson government should he push for no deal. The chancellor said it was “absolutely necessary” for the UK to extend its EU membership beyond 31 October.

Asked whether he would rule out voting in favour of a no-confidence motion against Johnson, he told Le Monde and Süddeutsche Zeitung: “I will take steps to avoid an exit without agreement apart from an explicit parliamentary approval. There should be a new and sincere attempt to reach a consensus. If we do not find a solution with the members, we may have to ask the British to give their opinion again in one form or another.”

Asked again to rule out supporting a motion of no confidence, Hammond responded: “I do not exclude anything for the moment.”

This week the European commission president-designate, Ursula von der Leyen, said she was open to a further Brexit extension.

The French president, Emmanuel Macron, has been consistently tough on the issue and would be likely to question whether the UK’s continued membership with Johnson in Downing Street would serve the EU well, but Berlin remains determined to avoid the economic damage of Britain crashing out.

On Friday Angela Merkel said the withdrawal agreement struck by Theresa May would not be revised but it remained possible to redraft the political declaration in such a way that the Irish backstop would be defunct.

“The withdrawal agreement is the withdrawal agreement,” Merkel told a news conference. “But the moment that a solution for the management of the border is found in [the declaration on] the future relationship … which basically squares the circle – on the one hand no physical border but on the other hand the EU single market ends – then the backstop will be overwritten, so to speak.”

Merkel added: “This means the task is to draft future relations that way and perhaps to draft them more specifically and better and more precisely than so far.”

Senior EU sources said discussions had been held on how to manage the 24 hours before a no-deal Brexit should it happen. The belief voiced in Paris that the UK would react to the economic shock by urgently seeking to reopen talks is not shared by a number of member states that would be most directly affected by a no-deal departure.

“There is the worry among some that a kind of wartime spirit will take over, but we have to put out a hand to Britain,” said one EU diplomat.

On Friday Alberto Costa, a Conservative MP who is fighting to secure post-Brexit rights for EU citizens in the UK and UK citizens in the EU, led a delegation to meet the EU’s chief negotiator, Michel Barnier.

Costa said: “He made very clear that the European commission has at its very top of the political agenda the protection of citizens’ rights and it will continue to do everything it can to protect the rights of those 5 million citizens even in the absence of a withdrawal agreement.”