The transition accord was announced Monday at a news conference in Brussels by David Davis, Britain's main negotiator, and his European Union counterpart, Michel Barnier, who described it as a "decisive step" toward an orderly withdrawal, or Brexit.
At first glance, the terms of the transitional phase fit precisely the recipe set down by the EU's chief negotiator Michel Barnier - a 21-month "status quo" period during which the rest of the world carries on treating the United Kingdom as if it were still a member of the bloc. The Theresa May government reached an agreement on Brexit after making a series of concessions to Brussels, where the European Union is headquartered, and accepting a "back stop" plan to keep Northern Ireland under European law and avoid a hard border with the Republic of Ireland.
After intense rounds of talks, David Davis, the Brexit secretary, said, "The agreement on the terms of the 21-month period, ending on December 31, 2020, was a significant moment, which would give businesses and citizens the reassurance they needed". But Dublin wants this year's treaty to lock in a "backstop" or fallback arrangement in case that future agreement does not work.
However, "the transitional period will only come after everything is agreed", said Barnier.
The talks have focused on reaching agreement on the transition phase, during which Britain will follow European Union rules until from when it leaves the bloc in March 2019 at least the end of 2020, in a bid to ease the shock of its departure.
"A decisive step remains a step, we are not at the end of the road and there is a lot of work still to be done on important subjects including Ireland and Northern Ireland".
"It remains our intention to achieve a partnership that is so close as to not require specific measures", Davis said on Monday, insisting on a solution "that is acceptable to both sides".
Davis agreed with Barnier that Monday's agreement was "decisive" and increased the odds on finding an orderly deal to avoid Europe's second biggest economy simply crashing out of the bloc in just over a year.
He said that negotiators, working day and night recently, had agreed on "a large part of what would constitute" the draft global legal agreement governing Britain's departure. "And this option will allow citizens who so wish, to have immediate legal certainty on their right of residence after the transition period", said Barnier.
The border between European Union member state Ireland and Britain's territory Northern Ireland issue is central to an agreement but negotiators are struggling to find a way to keep people, goods and services flowing while respecting European Union controls.
The most eloquent response to Monday's agreement on a Brexit transition deal was the silence of the Brexiteers on Theresa May's backbenches.