There should be the greatest possible transparency over the legal advice that has led the Government to determine new legislation on the Northern Ireland Protocol will not breach international law, opposition parties have said.

Northern Ireland Secretary Brandon Lewis committed to publishing the Government’s “legal position” on the matter on Monday, when the Bill is due to be introduced to Parliament, but insisted “governments don’t publish details behind advice given to ministers”.

Downing Street has said it will share only “a summary” of the legal advice it received with the public, which has led to accusations of a “cover-up”.

The legislation will give ministers powers to override parts of the protocol – a move the EU has warned could prompt retaliatory action.

A No 10 spokesman said on Friday: “The Bill has been agreed by the relevant cabinet committees and will be introduced to Parliament on Monday.

“We will, alongside the Bill, publish a summary of the legal advice.”

Labour’s shadow Northern Ireland secretary, Peter Kyle, said it is “incumbent on ministers” to release the maximum possible legal advice, with “transparency about its origins”.

“This Bill could have an elevated impact on Britain’s relationship with global partners, and has potential for malicious and rogue governments to interpret it as a green light for unilateral action against international treaties to which they are bound,” he said.

“Given this, it is incumbent on ministers to release the maximum possible legal advice from the start, with transparency about its origins, so the legal basis upon which they make their case to Parliament can be judged.”

Liberal Democrat Northern Ireland spokesman Alistair Carmichael said the public deserves “full transparency” over the plan’s legal basis, saying he suspects a “cover-up”.

“The Government must come clean and publish what legal advice was received and who from, in full,” he said.

“The public deserves full transparency over the legality of plans to rip up the Northern Ireland Protocol and risk a trade war with our closest neighbours. If Conservative ministers have nothing to fear, they have nothing to hide.”

Mr Lewis told Sky News’ Sophy Ridge On Sunday the new legislation to be outlined on Monday “is within the law”.

“What we’re going to do is lawful and it is correct,” he said.

“We will be setting out our legal position on this. People will see that what we’re proposing resolves the key issues within the protocol that don’t work.”

Asked why Downing Street was publishing only a summary of the legal advice, and not disclosing it in full, he told Times Radio: “Well, governments don’t publish details behind advice given to ministers, that’s part of … we have to have that free and open discussion as they’re formulating policy.

“But we are going to set out the Government’s legal position and our methodology for that.

“I think, again, when people see the legislation rather than some of these, people have picked up in titbits over the last few weeks, when they see the detail of the legislation, they’ll see we are acting within international law.”