Former Foreign Secretary Jeremy Hunt has issued a plea to EU foreign ministers to avoid a "catastrophic failure in statecraft" over Brexit.
He has urged them in an open letter to reach a compromise with Prime Minister Boris Johnson while they still can.
Delaying Brexit would only increase the chances of a no-deal exit, he warned.
"If they think this is bad - just wait until what happens after Boris wins an election," he told the BBC's Laura Kuenssberg in an exclusive interview.
Mr Hunt - who lost out to Mr Johnson in July's Conservative leadership contest - has written to the 27 EU foreign ministers, urging them to show greater flexibility in talks with the UK.
In his interview with Laura Kuenssberg, he said: "I think we could be about to see a catastrophic failure in statecraft, not because of malevolence by the EU. I think they are sincere in wanting a deal.
"But just because they haven't really understood what's happening in British politics right now.
"And there is bureaucratic inertia. If you're trying to get 27 countries to agree a common position the easiest thing is always to do nothing. And that's the risk we face."
In his 1st big Brexit intervention from Jeremy Hunt since he left Foreign sec job - urges EU to avoid a ‘historic miscalculation’ , writing to his former counterparts around the continent - our interview on #bbcnewsten in a min pic.twitter.com/08Hiqgs24I— Laura Kuenssberg (@bbclaurak) October 9, 2019
Mr Hunt, who backed Remain in the 2016 EU referendum but went on to be a strong supporter of Mrs May's withdrawal agreement, quit the cabinet in July after Mr Johnson attempted to remove him as foreign secretary.
He told the BBC Mr Johnson had made mistakes in his handling of Brexit, although he declined to say what they were, but stressed they both agreed on the need for a speedy resolution to Brexit.
He argued that the EU had been guilty of misreading the political situation in the UK in the past - over David Cameron's ill-fated renegotiation attempt in 2015 and Theresa May's withdrawal agreement - and could do so again.
"My worry is that they're about to make the same profound miscalculation that 'oh we can just hang tight, see if there's an election and if Boris Johnson wins it we can negotiate on the same deal but if he doesn't, so much the better because maybe we'll have a second referendum.'
"If Boris wins, which is what the polls are saying, at the moment, and he comes back with a majority, that British government will be much less willing to compromise," he said.
This, he argues in his open letter to his former EU colleagues, will make a no-deal Brexit more likely - an outcome they had always agreed it was "vital" to avoid.
"I fear a profound and mutual lack of understanding is leading the EU to make the same mistakes over and over again," he writes.
"I am hoping and praying that does not happen because the implications for our future relationship would be extremely grave."
Mr Johnson has said he remains "cautiously optimistic" about a deal, while continuing to insist the UK will leave on 31 October with or without an agreement.
He is set to meet his Irish counterpart, Leo Varadkar, on Thursday to try and break the deadlock.
Mr Varadkar has expressed concern about Mr Johnson's proposal to give the Northern Ireland Assembly a vote over entering into a "regulatory zone" with the EU, which would involve it leaving the customs union.
Mr Hunt said: "I'm sure they would love to keep Northern Ireland in the single market and customs union in perpetuity.
"But in the end, that is not going to work for the UK, I don't think this is just the strong supporters of Boris Johnson who feel this, this would be to divide up a sovereign country, and that wouldn't be acceptable I don't think any other country in Europe either."
He urged Ireland to take a "statesmanlike approach at this stage" adding that there was a "deal to be done which prevents a hard border on the island of Ireland, which allows regulatory alignment, the smooth flow of people and products across that border, which is so important for the Belfast Good Friday Agreement, it's going to need compromise on all sides".
He added: "It's Ireland's call now because I don't think that the EU are going to budge unless they get that signal from Varadkar."