THERESA May has warned moves to scrap unilaterally parts of Northern Ireland’s Brexit deal are “not legal” and will “diminish” the UK’s global standing.

The Tory former prime minister delivered a withering assessment of the Northern Ireland Protocol Bill as she made clear she would not support it.

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 House of 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.”

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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.

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 has angered unionists.

But capitals across the EU bloc reacted with outrage to the plans to override parts of the protocol, amid concerns it breaches international law.

May said she did not believe the Bill would achieve the aim of restoring powersharing institutions at Stormont and warned it would give UK ministers “extraordinarily sweeping powers”.

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.”

May also expressed doubt that the Bill will bring the EU back to the negotiating table.

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In the same debate, Richard Thomson, SNP MP for Gordon, said the UK Government would stand a much better chance of success if its negotiations with the EU were based on “trust”, “good faith” and “co-operation”.

The SNP Northern Ireland spokesman said: “We need a protocol, the nature of Brexit means there needs to be a protocol.

“It doesn’t need to be exactly the same as this version, but what we absolutely don’t need in the middle of a cost-of-living crisis is a prospect of increased trade frictions through needless conflict and a developing trade war with our largest overseas and closest market.

“That, I very much fear this legislation, if enacted and utilised, would do.”

He added: “We need negotiations which are based on trust, which are based in good faith, which are based on co-operation. I think the UK Government would stand a much, much better chance of success if it were driven by this instead of this piece of legislative brinkmanship.

“Also, if it were to pursue measures for once which were motivated by a genuine desire to deliver the best possible outcome out of this mess for all peoples in these islands, rather than simply pandering to the agendas of those … the tiny subset of the population that might have an influence over who the next leader of the Conservative and Unionist Party may happen to be.”