Boris Johnson is facing a growing Tory backlash over controversial plans to override key elements of his Brexit deal with Brussels, in breach of international law.

MPs reacted angrily after Northern Ireland Secretary Brandon Lewis said on Tuesday that legislation to change the Withdrawal Agreement would go against international law in a “very specific and limited way”.

Ministers have argued the measures are necessary to ensure “damaging” tariffs are not imposed by “default” on goods travelling from the rest of the UK to Northern Ireland if negotiations with the EU on a free trade agreement fail.

But a series of senior Conservatives have expressed dismay, warning the move risks undermining Britain’s standing and reputation as an upholder of international law.

Tobias Ellwood, chairman of the Commons Defence Committee, said that if the Government went through with the changes to the agreement – which secured the UK’s departure from the EU in January – it would “lose the moral high ground”.

“This is about the rule of law and our resolve and commitment to uphold it,” he told the BBC Radio 4 Today programme.

“To unilaterally ignore any treaty in its obligations which we’ve signed and submitted to the United Nations would actually go against everything we believe in.”

“How can we look at countries such as China in the eye and complain about them breaching international obligations over Hong Kong, or indeed Russia over ballistic missiles, or indeed Iran over the nuclear deal if we go down this road?”

He suggested there was an element of “sabre-rattling” as negotiations on a free trade deal approached the final stages with both sides apparently deadlocked.

His comments echoed Tom Tugendhat, chairman of the Commons Foreign Affairs Committee, who said Britain had traditionally been the “chief exporter” of the rule of law around the world.

“We have been the single pillar of dependability in international negotiations… which has allowed others to prosper and indeed allowed us to prosper,” he told a British Foreign Policy Group think tank event on Tuesday.

“It’s not just about the law. Our entire economy is based on the perception that people have of the UK’s adherence to the rule of law.”

The warnings – following similar concerns expressed by former prime minister Theresa May – came as ministers tabled the Internal Market Bill containing the changes in the Commons on Wednesday.

The Prime Minister defended his plan after SNP Westminster leader Ian Blackford accused him of “creating a rogue state” where the rule of law does not apply.

Mr Johnson told Prime Minister’s Questions the Bill is “about protecting jobs, protecting growth, ensuring the fluidity and safety of our UK internal market and prosperity throughout the UK”.

Mr Lewis had said it would “dis-apply” the EU legal concept of “direct effect” in the Withdrawal Agreement which would require the UK to continue to uphold EU law in relation to Northern Ireland customs arrangements.

Lord Darroch, the former British ambassador to United States who was forced to resign after his diplomatic cables criticising Donald Trump were leaked to the press, suggested the Prime Minister was adopting the tactics of the US president.

He said Mr Johnson, when he was foreign secretary, had privately suggested that if Mr Trump was negotiating a Brexit deal he would create “all sorts of chaos” at the start in order to achieve a “very good outcome” at the end.

“Now as I watch him and the Government conduct the post-withdrawal future relationship arrangements, I just wonder if there’s an aspect of the way Donald Trump would have done it and how he is doing it,” he told BBC2’s Newsnight.

However Health Secretary Matt Hancock insisted the changes were necessary to protect the Northern Ireland peace process if they failed to get a free trade deal with the EU.

“The decision we’ve made is to put the peace process first, first and foremost as our absolute top international obligation,” he told the Today programme.