Boris Johnson has referred to the Treasury as the “heart of Remain” and called for “guts” in Brexit talks in comments made at a private dinner.
The foreign secretary also warned there may be a Brexit “meltdown”, according to a recording obtained by 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 he had been recorded.
The foreign secretary was apparently speaking to around 20 people in a private room after an Institute of Directors reception on Wednesday night.
- Trump-Kim summit: North Korea leader may get US invite
- UK publishes customs plan after crunch talks
- What’s the big picture behind Brexit ‘backstop’ drama?
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.”
‘Tail wagging the dog’
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.”
The comments emerged after a day which saw the prime minister involved in a cabinet row over the government’s “backstop” plan on customs.
By Chris Mason, BBC political correspondent
The sentiments expressed might be unsurprising, but in colourful language and with devastating timing, Boris Johnson becomes the second cabinet minister in 24 hours to throw the prime minister’s authority into the pestle and mortar and pummel away.
His friends say he’s disappointed the remarks were covertly recorded.
But it’s not surprising they were.
So first there was the Brexit Secretary hokey cokey: David Davis saying it is my way or the stairway (to the backbenches), and doing so in a way where, depending whether it was 10:00 or 11:00, he was either in the cabinet or about to be out.
And now this. Johnsonian expression, including obligatory flourishes in Latin, which amounts to the same thing: a flexing of Brexiteer muscle in the direction of a prime minister desperate to hold her cabinet, her party and the country together.
It’s one heck of a job.
‘Method in Trump’s madness’
Mr Johnson was the keynote speaker at Conservative Way Forward’s summer reception and took questions for more than an hour – with other Conservative MPs, including Priti Patel and Conor Burns, present – according to Buzzfeed.
Asked about Donald Trump, he said he was “increasingly admiring” of the US President, 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.”
Mr Johnson’s other comments included:
- Russia’s importance had greatly diminished and its economy was now the size of Australia
- Russian President Vladimir Putin wanted to cause trouble and “upset people like us”
- The UK needed to engage with China, who he predicted would eventually take over as the world’s technology giant
- He would love to visit North Korea but has no immediate plans to do so