The Government must act to prevent Northern Ireland becoming a magnet for asylum seekers, the interim leader of the DUP has said.

Gavin Robinson was commenting after a judge in Belfast ruled that much of the UK’s Illegal Migration Act could not apply in Northern Ireland due to rights protections that are guaranteed under the post-Brexit Windsor Framework.

Mr Robinson warned the Government that it must not facilitate the creation of an “immigration border” in the Irish Sea, with different rules applying in Northern Ireland to the rest of the UK.

The ruling delivered in the High Court on Monday would disapply large sections of the Act in Northern Ireland.

A central plank of the new laws is a scheme that would see asylum seekers deemed to have arrived illegally in the UK detained and removed to Rwanda.

Mr Robinson insisted that his party had repeatedly warned the Government that its immigrations laws were incompatible with post-Brexit arrangements contained in the Northern Ireland Protocol/Windsor Framework.

“Whilst today’s judgment does not come as a surprise, it does blow the Government’s irrational claims that the Rwanda scheme could extend equally to Northern Ireland completely out of the water,” he said.

“We presented the Government with an opportunity during the passage of the Safety of Rwanda Bill in the House of Commons and the Lords to accept an amendment which would have put beyond doubt what it claims to be the case around the operation of the scheme.

“It is telling that it chose not to do so.

“This ruling must also mark a watershed moment in the Government’s approach.

“For Ministers to ignore what the courts have said would not be merely a case of sleepwalking into the creation of immigration border in the Irish Sea but rather embarking on such a path with eyes wide open.

“It is imperative that immigration policy applies equally across every part of the United Kingdom.

“As unionists, we are clear that our national parliament should have the ability to make decisions on immigration that are applicable on a national basis.

“If that were not the case, it would not only be a constitutional affront but would make Northern Ireland a magnet for asylum seekers seeking to escape enforcement.”

The Windsor Framework offers a guarantee that there will be no diminution of the rights provided for within the Good Friday peace agreement of 1998.

Delivering his court judgment, Mr Justice Humphreys ruled that a several sections of the Illegal Migration Act would lead to a diminution of the rights of asylum seekers residing in Northern Ireland.

DUP deputy First Minister Emma Little-Pengelly told the Stormont Assembly on Monday that the Government needed to ensure that Parliament asserted its sovereignty by addressing the issues raised in the judgment.

“I think the High Court has been very clear today,” she said, noting she was speaking in a personal capacity.

“The UK government in my view, now this matter may well go to the Supreme Court, but the UK Government must in my view take cognisance of what the High Court has said and move to urgently address these issues.

“Because the UK Parliament has sovereignty over these issues.

“They have asserted that sovereignty over these issues, so they should use that sovereignty to address these issues emerging from the no diminution of rights wider scope and implications as set out in the judgment today.”

TUV leader Jim Allister criticised the DUP for agreeing to return to devolution at Stormont earlier this year on the basis of the Government’s Safeguarding the Union command paper – a document that insisted that the application of UK immigration policy in Northern Ireland would not be affected by post-Brexit arrangements agreed with Brussels.

“Yet another humiliation and savaging of UK sovereignty as NI is again found to be an EU colony where the writ of Brussels, not London, runs,” said Mr Allister.

“Here again the DUP’s ‘Safeguarding the Union’ document is exposed as a sham as its promises in paragraph 46 that the Rwanda Bill is untouched by the Protocol are shredded by the High Court.

“Now we not only have a trade partitioning Irish Sea border, but now an immigration border too, leaving NI wide open as a magnet for asylum seekers.

“It’s time the DUP disavowed its sell out document and got on the side of demanding, not diminishing, British sovereignty.”