Boris Johnson has ridiculed fears over the border in Ireland, warned that a final Brexit deal will violate Leavers' red lines and acknowledged "there may be a meltdown" during negotiations during an explosive private conversation earlier this week.

Speaking to a select group of party activists during a private dinner with pressure group Conservative Way Forward, the foreign secretary admitted there was a high chance of Britain ending up with terms that would cross his and other Brexiters' red lines.

During a dinner on Wednesday, Johnson told a group of 20 or so Thatcherite activists the way talks were going the UK could be kept “locked in orbit around the EU, in the customs union and to a large extent still in the single market,” according to a series of recordings leaked to Buzzfeed last night.

That would mean “not really having full freedom on our trade policy, our tariff schedules, and not having freedom with our regulatory framework either," the minister said.

He accused the Treasury of being “basically the heart of Remain” and driving the agenda to stay closer to Brussels longer term. However Johnson said he would be willing to accept staying close to the EU for longer than March 2019.

“I will be prepared to compromise over time, but I will not compromise over the destination,” he said.

Remainers fear "short-term" disruption to the economy because of friction at the borders, Johnson claimed. "So theyre sacrificing all the medium and long-term gains out of fear of short-term disruption. Do you see what Im saying? The fear of short-term disruption has become so huge in peoples minds that theyve turned into a quivering wreck.”

“Theyre terrified of this nonsense,” Johnson said. “Its mumbo jumbo.”

While he acknowledged there would be "bumps in the road", he played down the "prophecies of doom", insisting they were “pure millennium bug stuff".

“All the planes crashing from the sky. Its absolute nonsense.”

He added: “Unless you make the change, unless you have the guts to go for the independent policy, youre never going to get the economic benefits of Brexit. Youll never get the political benefits of Brexit.”

On the matter of the Irish border, the foreign secretary claimed the government was "allowing the tail to wag the dog", adding: "Were allowing the whole of our agenda to be dictated by this folly.”

And he made the case for max fac once again, rubbishing HMRC boss Jon Thompson's estimate that it would cost businesses £20bn a year and saying a solution was "not beyond the wit of man".

But he warned activists things would get worse before they got better.

“I think Theresa is going to go into a phase where we are much more combative with Brussels,” he said.

“Youve got to face the fact there may now be a meltdown. OK? I dont want anybody to panic during the meltdown. No panic. Pro bono publico, no bloody panic. Its going to be all right in the end.”