The Foreign Secretary insisted it was possible to get a revised deal with Brussels by the end of September, and said if it took "a few extra days" to get it through parliament he would delay Brexit beyond the 31 October deadline. "In order to close down parliament the prime minister would have to go to her Majesty the Queen and ask for her permission to prorogue", he said.
His rival for the leadership, Foreign Secretary Jeremy Hunt, said Sir Kim had made it clear that Mr Johnson's comments were a factor in his decision to quit.
Speaking at a leadership hustings in Cheltenham, Mr Hunt said: "Maybe I will pay a political price for being honest with people".
Johnson said it was "manifestly in the interests of both sides" to reach a new deal, noting "the European Union has a very substantial net balance of trade with us".
"I if truth be told mediate there is somewhat a dissimilarity between Parliament and the public", she said.
Asked whether he would be prepared to delay by days, weeks or months, Mr Hunt replied: 'Well, it's not going to be months'.
But pressed on whether the United Kingdom would be out by Christmas, he said: "I'm not going to give you those commitments".More news: Amazon delays Vesta, its household surveillance robot
More news: Special counsel Robert Mueller's hearing could be delayed
More news: 7-Eleven giving away free Slurpees on 7/11
His warning came as peers tabled an amendment to government legislation in the House of Lords that would stop Johnson from shutting parliament down in the autumn to stop MPs blocking no-deal. If you value what we are doing, you can help us by making a contribution to the cost of our journalism.
"I think it'll be a mixture of pride at having done the job but also a degree of disappointment because there was more that I wanted to do", she told the BBC on Friday.
But leading Eurosceptic Tory MP Andrew Bridgen lambasted them, saying: "We need to leave by October 31 and quite honestly, people like Greg Clark and Philip Hammond have been roadblocks to preparing for no deal".
The fact that Johnson, who is expected to become the next PM, didn't support the ambassador was one of the reasons he stood down, says Dr Farr, as he added that effectively, the next PM sided with the foreign government over one of his own representatives in what is an extraordinary situation. We then delayed it for a further six months. Everyone knows that." "I think that every person who considers the evidence that companies have given, whether it's in the automotive sector, whether it's in the food sector, whether it's in aerospace, whether it's in industries up and down the country.
He claimed there was an "outbreak of common sense" beginning to take place within the Tory party and across Parliament - with people "coming together to get this thing done".
Mr Johnson did not answer questions about whether he still believed Donald Trump was "stupefyingly ignorant" - in reference to comments he made as London mayor - and came unstuck when grilled on the detail of world trade rules.
"You know if you become less efficient and your ability to trade is impeded then, of course, losing your competitiveness means that there will be jobs that will be lost".