The move by the DUP threw into chaos plans to move onto the second stage of Brexit talks, about trade arrangements and a transition period for Britain’s departure from the EU, by December 14.
It was followed by calls from Nicola Sturgeon, the first minister of Scotland, and Sadiq Khan, the Mayor of London, for similar separate arrangements for other parts of the United Kingdom that voted to remain in the EU.
Mrs May was accused of trying to “bounce” the Cabinet into agreeing to “regulatory alignment” between Ulster and Ireland after it emerged she did not brief senior ministers before talks in Brussels on Monday that stalled over the controversial issue.
Mr Johnson on Wednesday defended Mrs May’s “very good” offer to settle the so-called Brexit bill, which is expected to amount to up to £50 billion, and said Britain should be “punctilious” about paying reasonable obligations.
“I was asked my reaction to some of the very extortionate sums that I had heard in the region of £80 or £100 billion, and, I don;t want to repeat the offending phrase, but go whistle seems the appropriate reaction to that kind of sum.”