The ministers' official legal advice is that overwriting key parts of the Brexit divorce deal would violate international law, Secretary of State Brandon Lewis said.
Mr Lewis told MPs that his claim was "absolutely in line" with the views of the top lawyers advising the UK government.
He said he gave a "clear" and specific answer last week to a question on the UK Internal Market Act which gives ministers the power to override provisions of the readmission agreement relating to Northern Ireland.
The minister said: "I gave Parliament a very clear answer last week, in line with the position of the Attorney General.
"My position is absolutely in line with the legal advice given by the Attorney General."
Secretary of State Brandon Lewis (left) screengrab from Parliamentary TV alongside Colin Perry, Northern Ireland Commercial Director, video-linked to the Northern Ireland Affairs Committee in the House of Commons. Image by Parliament TV / PA Wire
Mr Lewis sparked a backlash after admitting that steps by the UK government regarding the withdrawal agreement would violate international law in "specific and limited ways".
He broadened the scope of his comments when he practically appeared before the Northern Ireland Committee of Representatives today.
He said, "I read something very specific because I wanted to make sure what I was saying … to make sure I give the House a clear answer."
He told MPs his claims are in line with the advice of the UK Government's key legal advisor, Attorney General Suella Braverman QC.
He said: "My answer was in line with the judicial officers' legal opinion.
"The position I took on the mailing box is not a violation of the Ministerial Code, but I am not the arbiter for it."
The Single Market Act affects the Northern Ireland Protocol – part of the EU withdrawal agreement, which aims to prevent a hard border from returning to the island of Ireland after Brexit if a trade deal is not reached.
The law aims to ensure that Northern Ireland's compliance with EU customs rules does not affect the country's tradability with the rest of the UK.
Areas such as the eligibility of state aid for producers and the precise nature of the formalities or customs controls related to the exit were discussed during the negotiations with Brussels.
Mr Lewis said the protocol will always be subordinate to the UK and EU joint committee which will work out details of the future relationship and ensure Northern Ireland full access to UK trade.
A government chief legal officer said the Northern Ireland secretary "answered the wrong question" when speaking on international law.
The UK's Single Market Act is not a "violation of international law or the rule of law," Lord Keen of Elie, the Advocate General for Scotland, recently told colleagues in the House of Lords.
Northern Ireland Conservative Committee chairman Simon Hoare said much of the "steam and concern" about the possible violation of an international treaty could have been avoided.
He added, "This appears to have been a rather clumsy elephant trap that they created that might have been avoided."
Claire Hanna, SDLP MP from South Belfast, challenged Mr Lewis.
She said, "Do you understand why the people of your government cannot trust your government and are you connected with the fear, discomfort and instability your government causes in Northern Ireland every day?"
The MP for Great Yarmouth said he disagreed.
Conservative MP Robert Goodwill asked if someone at 10 Downing Street, who was checking the name of top aide, Dominic Cummings, had written the line about violations of international law.
Mr Lewis said he would not comment on who had written advice.
"We all wanted to make sure we gave the house a straight answer."
Despite the heated rhetoric on both sides of the post-Brexit talks, Mr Lewis insisted that he believed the EU was acting in "good faith" during the negotiations and did not believe that the dispute over the UK's single market law would derail talks would let.
He added, "I think the negotiators on both sides are very capable of focusing on negotiating."
(tagsToTranslate) Brexit (t) Internal Market Bill (t) Brandon Lewis