Boris Johnson 'warns of Brexit meltdown'

The foreign secretary also referred to the Treasury as the "heart of Remain", according to Buzzfeed.

Speaking to campaign group Conservative Way Forward, he said fear of initial disruption meant the Treasury was sacrificing long-term gains.

Friends of Mr Johnson said they were disappointed remarks made at a private event had been covertly recorded.

The foreign secretary was apparently speaking to around 20 people in a private room after an Institute of Directors reception on Wednesday night.

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According to Buzzfeed, he said that the prime minister was "going to go into a phase where we are much more combative with Brussels".

He added: "You've got to face the fact there may now be a meltdown. OK? I don't want anybody to panic during the meltdown. No panic. Pro bono publico, no bloody panic. It's going to be all right in the end."

Brexit will be "irreversible" and will happen, Mr Johnson said, but the "risk is that it will not be the one we want".

He added: "Unless you make the change, unless you have the guts to go for the independent policy, you're never going to get the economic benefits of Brexit. You'll never get the political benefits of Brexit."

BBC political editor Laura Kuenssberg said Mr Johnson's comments were not surprising - and neither was the fact they were leaked.

She said: "Frankly, it's not just guts that Theresa May needs, but all the help she can get.

"And if the last 24 hours are anything to go by, that help is not coming from all of her colleagues."

He was said to have described concerns over the border between Northern Ireland and the Irish Republic as "pure millennium bug stuff" and suggested Chancellor Philip Hammond's department was "basically the heart of Remain".

Mr Johnson said fears about the Irish border were out of proportion, saying: "It's so small and there are so few firms that actually use that border regularly, it's just beyond belief that we're allowing the tail to wag the dog in this way."

Speaking about the Treasury, he added: "They don't want any disruption of the economy. So they're sacrificing all the medium and long-term gains out of fear of short-term disruption."

He also said he was "increasingly admiring of Donald Trump", who is preparing for an historic summit with North Korea's leader Kim Jong-un.

Mr Johnson was reported to have said: "I have become more and more convinced that there is method in his madness."

"Imagine Trump doing Brexit," he added.

"He'd go in bloody hard... There'd be all sorts of breakdowns, all sorts of chaos. Everyone would think he'd gone mad. But actually you might get somewhere.

"It's a very, very good thought."

He said he was "increasingly admiring" of Donald Trump.