BREXIT FUTURE
Frost, a former diplomat who was repeatedly hailed by Johnson as "the greatest Frost since the Great Frost of 1709," was a committed Brexit supporter who negotiated Johnson's revised EU divorce deal and a trade agreement.
He cast the United Kingdom's 2016 vote to leave the EU as part of a broader rebellion against the bloc's transnational collective governance that wanted to revive the nation-state.
Having such a true "Brexit believer" at the heart of British power gave reassurance to Brexit supporters in the Conservative Party that Johnson would remain tough on the European Union.
Frost, until his resignation, was leading an attempt by London to renegotiate parts of the divorce deal concerning Northern Ireland.
Beyond Brexit, though, the 56 year-old Frost was unhappy.
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In a speech last month, Frost expressed his clear discontent with the course of post-Brexit British policy.
"We have not successfully rolled back the frontiers of the European Union from Britain with Brexit, only to import that European model after all this time," Frost said in a Nov. 22 speech at the Margaret Thatcher Conference on Trade.
He disagreed with "those who think we can treat the private sector as just a convenient way of keeping the public sector running."
"It isn't just a source of taxes," Frost said. "We can't carry on as we were before, and if after Brexit all we do is import the European social model we will not succeed."
The opposition Labour Party said the government was in chaos and said Johnson should provide clarity on what would happen in talks with the EU over the Northern Irish Protocol, a part of the divorce deal.
"Boris Johnson needs to get a grip, tell us his plan for the next few weeks and bring certainty for the people of Northern Ireland by unblocking the stalemate over the Protocol," said Jenny Chapman, Labour's shadow minister of state at the Cabinet Office.