The PM’s bid to unilaterally scrap elements of the Northern Ireland protocol, part of Johnson’s Brexit withdrawal deal with the European Union in 2019, cleared its first Commons hurdle on Monday night.
MPs voted 295 to 221, majority 74, to give the key legislation a second reading.
The division list showed no Conservative MPs voted against it – despite unease among some backbenchers, as underlined by May’s comments. Some 283 Tory MPs supported the bill along with eight DUP MPs.
Given the widespread unrest with the Johnson within the party, a Tory rebellion may yet emerge as the bill makes its journey through parliament.
The UK government has argued the measures to remove checks on goods and animal and plant products travelling from Great Britain to Northern Ireland are necessary to safeguard the Good Friday Agreement and peace and stability.
The imposition of checks between Great Britain and Northern Ireland in order to keep an open border with Ireland – effectively drawing a line in the Irish Sea – has angered unionists.
But capitals across the EU bloc reacted with outrage to the plans to change parts of the agreement, amid concerns it breaches international law. Brussels has also not agreed to re-open negotiations.
Ahead of the vote on Monday, former prime minister May – who was brought down over Brexit and tensions surrounding the border – called into question Johnson’s patriotism as she made clear she would not support the Northern Ireland Protocol Bill.
May questioned the argument that a legal principle of necessity allows for the UK government’s plans, insisting there is “nothing urgent” about the legislation.
Concluding her speech to the Commons, she said: “The UK’s standing in the world, our ability to convene and encourage others in the defence of our shared values, depends on the respect others have for us as a country, a country that keeps its word, and displays those shared values in its actions.
“As a patriot, I would not want to do anything that would diminish this country in the eyes of the world.
“I have to say to the government, this bill is not, in my view, legal in international law, it will not achieve its aims, and it will diminish the standing of the United Kingdom in the eyes of the world, and I cannot support it.”
Foreign secretary Liz Truss had earlier attempted to downplay concerns of MPs by arguing the bill has a “strong legal justification” and the UK remains committed to seeking a negotiated solution.
Speaking during the bill’s second reading, she said: “I actually started off by asking myself three questions: First of all, do I consider this to be legal under international law? Second, will it achieve its aims?
“Third, does it at least maintain the standing of the UK in the eyes of the world? My answer to all three of those questions is ‘no’.
“That is even before we look at the extraordinarily sweeping powers that this Bill would give to ministers.”
Story was updated following the vote.