Just 22 Conservatives voted against Mr Sunak's compromise to end the deadlock on the Northern Ireland protocol in a blow to the former prime minister's authority.
Mr Johnson announced that he would join the DUP in rejecting the so-called "Stormont brake", describing Mr Sunak's deal as "unacceptable".
But in a huge relief for Mr Sunak, MPs voted in favour of the Stormont brake by an overwhelming 515 to 29, meaning the government did not have to rely on Labour votes.
The DUP voted against the deal and the European Research Group (ERG) of Tory Brexiteers had "strongly recommended" its members oppose the Windsor deal.
Mr Johnson was joined by former Tory leaders Liz Truss and Iain Duncan Smith in voting against the deal struck by Mr Sunak and EU Commission president Ursula von der Leyen.
Loyal Johnson allies Priti Patel, Jacob Rees-Mogg, Jonathan Gullis and Jacob Berry joined Truss loyalist Simon Clarke and more than a dozen hardliner ERG members - including David Jones, William Cash, Peter Bone and John Redwood - in voting against the deal.
In blue-on-blue Brexiteer infighting yesterday, Northern Ireland minister Steve Baker attacked Mr Johnson's opposition and said he risked looking like a "pound shop Nigel Farage".
This story is from the March 23, 2023 edition of The Independent.
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This story is from the March 23, 2023 edition of The Independent.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 8,500+ magazines and newspapers.
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