Prime Minister Theresa May's foreign minister and Brexit negotiator quit on Monday in protest at her plans to keep close trade ties with the European Union after Britain leaves the bloc, stirring rebellion in her party's ranks.
In his resignation letter, he said the Brexit "dream is dying, suffocated by needless self-doubt".
"We are truly headed for the status of a colony - and many will struggle to see the economic or political advantage of that particular arrangement", Johnson said in a resignation statement.
Johnson quit on Monday over May's plan for Brexit, which includes a free-trade area for goods but little detail on the approach to services.
With Britain due to leave the 28-nation bloc on March 29, 2019, European Union officials have warned Britain repeatedly that time is running out to seal a deal spelling out the terms of the divorce and a post-split relationship.
Hamilton vows to move on after Raikkonen apology Only 14 cars finished the race, with both Sauber cars stopping early as well as Red Bull's Max Verstappen retiring after 46 laps. Sebastian Vettel in the post-qualifying press conference at the 2018 British Grand Prix at Silverstone .
The announcement came half an hour before the Prime Minister was due to address MPs on the Cabinet agreement reached at Chequers last week, and a few hours before a crucial appearance before the 1922 Committee of Conservative MPs which could decide her fate.
She told her critics the alternative to the party coming together could be a left wing Labour administration, with Jeremy Corbyn as prime minister.
Brexit-backing lawmakers have been angered by May's plans, saying they will keep Britain too close to the European Union and limit its ability to strike new trade deals.
"In the two years since the referendum, we have had a spirited national debate, with robust views echoing around the cabinet table as they have on breakfast tables up and down the country", she said. "I won't be encouraging people to do that, I think it's the wrong thing to do".
Under Conservative Party rules, a confidence vote in a leader can be triggered if 48 lawmakers from May's Conservative Party request one.