The cornerstone of Rishi Sunak’s Rwanda deportation policy should not apply in Northern Ireland because it undermines human rights protections guaranteed in the region under post-Brexit arrangements, a high court judge has ruled. Parts of the UK’s Illegal Migration Act were also incompatible with the European convention on human rights (ECHR), Mr Justice Humphreys said. The post-Brexit Windsor framework jointly agreed by the UK and EU says there can be no reduction in the rights provisions contained within Northern Ireland’s Good Friday peace agreement of 1998. But the court ruling on Monday found that provisions in the act resulted in a “diminution of rights” in Northern Ireland, including for asylum seekers resident there. The UK government is considering appealing against the ruling, which lawyers have warned could derail ministers’ plans to send thousands of asylum seekers to Rwanda. The Democratic Unionist party (DUP) said Downing Street had ignored its warnings about the legislation and that Northern Ireland risked becoming a magnet for asylum seekers. “It is imperative that immigration policy applies equally across every part of the United Kingdom,” said Gavin Robinson, the party’s interim leader. The Rwanda plan has also alarmed the Irish government, which says most asylum seekers to the republic come from the UK via Northern Ireland, leading to encampments in Dublin that have discomfited Simon Harris’s ruling coalition in the run-up to local and European elections. The ruling involved two cases, one taken by the Northern Ireland Human Rights Commission and the other by a 16-year-old asylum seeker from Iran who is living in Northern Ireland having arrived in the UK as an unaccompanied child. The boy arrived in Kent via a small boat and was transferred by the Home Office to Northern Ireland under a scheme to distribute lone child asylum seekers between different local authorities across the UK known as the national transfer scheme. The Illegal Migration Act prevents individuals who arrive into the UK via irregular means such as small boats from ever being able to claim asylum in the UK. Human rights lawyers said the judgment opened the possibility of discrimination challenges because the Illegal Migration Act now treats asylum seekers living in different parts of the UK differently. However, Sunak said the judgment would not derail the government’s Rwanda plans. The prime minister said: “This judgment changes nothing about our operational plans to send illegal migrants to Rwanda this July or the lawfulness of our Safety of Rwanda Act. We continue to work to get regular flights off to Rwanda in the coming weeks and nothing will distract us from that or delivering to the timetable I set out. We must start the flights to stop the boats. “I have been consistently clear that the commitments in the Belfast (Good Friday) agreement should be interpreted as they were always intended, and not expanded to cover issues like illegal migration. We will take all steps to defend that position, including through appeal.” While the asylum seekers currently detained for the first Rwanda flight, which is due to take off at the beginning of July, arrived before the Illegal Migration Act came into force and so are not directly affected by the judgment, future groups of asylum seekers targeted for forced removal to Rwanda could challenge their removals based on Monday’s ruling. Sinéad Marmion, the head of immigration and asylum at Phoenix Law and the solicitor in the case, said the Good Friday agreement remained a beacon of human rights protections and hope. “Today, the court through the Northern Ireland protocol, has ensured those rights apply to the whole community – including asylum seekers. This runs contrary to the negative and toxic rhetoric peddled by the government against those seeking international protection.” This judgment sent a clear message to the government, she said. “Not only will asylum seekers be welcome in Northern Ireland, but they will also be legally protected. Today marks the beginning of the end of the British government’s flagship campaign to enact illegal and immoral laws with the sole purpose of frustrating and demolishing international human rights protections.”