The Secretary of State for Northern Ireland has admitted that a new Bill that will change the Brexit Deal between the EU and UK will break international law.

Speaking in the House of Commons on Tuesday, Brandon Lewis said the Internal Market Bill would break international law in a “very specific and limited way”.

The Bill could affect trade and customs rules in post-Brexit Northern Ireland.

The leaders of four pro-Remain parties in Stormont – Sinn Féin, SDLP, Alliance and the Greens – said Downing Street must honour the Northern Ireland Protocol.

In an unsigned statement, the DUP welcomed “in broad terms” the new Bill.

The party said: “We note the speculation that the Government will pursue fall-back measures under the Internal Market Bill to protect Northern Ireland’s interests should a deal not be agreed that mitigates the threat of the NI Protocol.

“We will want to see the finer details and clauses relating to this, and will study them carefully.

“We welcome them in broad terms, in so far as they go, but the Government must continue to work to remove any disadvantages to Northern Ireland brought about by its signing up to the Protocol.”

The statement also said: “The DUP voted against the Withdrawal Agreement in Parliament. We were opposed to any concept that Northern Ireland’s economic place in the UK internal market should be compromised by the Protocol.

“On three occasions, we helped stop [then Prime Minister] Theresa May’s version of the Withdrawal Agreement, and we spoke against, argued against and voted against the current Prime Minister’s Brexit.

“We are still arguing that, in these negotiations, the Withdrawal Agreement must be scrapped or changed to take account of the need to protect Northern Ireland’s place in the internal market of the United Kingdom.”

Speaking from Stormont, Sinn Féin MLA Jemma Dolan expressed concerns about the moves of the British government to abandon the Withdrawal Agreement and Irish Protocol in the Brexit negotiations.

“This week ... we had reports of the British government preparing to abandon the Withdrawal Agreement and Irish Protocol and introduce its own legislation without any thought or regard for its impact on the North.

“This would be a betrayal of what has already been agreed and would inflict irreversible harm on our economy and the Good Friday Agreement.

“For some time now, the outlook on the future arrangements negotiations has been pessimistic, but this is a dangerous game that the British government is now playing.”

Miss Dolan said Sinn Féin’s priority is to avoid any border on the island of Ireland and to protect the Peace Process, Good Friday Agreement and all-Ireland economy.

She continued: “This must also remain a top priority for the EU and its member states. They must ensure the full and urgent implementation of the protocol which provides these safeguards is paramount.

“We will continue to defend the foundation stones of the Irish Peace Process, including the Good Friday Agreement, and work with those who share these priorities in the Assembly, Dáil, EU and United States Congress.”