Rishi Sunak’s government will present a full law to parliament to set aside the supreme court’s ban on sending asylum seekers to Rwanda, setting up a probable battle with MPs and peers and putting in doubt the aim for flights to begin leaving by spring. The law could be published within a fortnight, after next week’s autumn statement, and it will be primary legislation, meaning it will have to pass through all the normal stages of the Commons and Lords, Downing Street has said. “Certainly we want to do it as quickly as possible,” Sunak’s official spokesperson said, adding that progress would depend on other parties and the Commons speaker, Lindsay Hoyle. “I’m sure we will be engaging with all parts of the house as part of this.” Sunak announced the idea in a press conference on Wednesday after the unanimous supreme court ruling against the plan, saying emergency legislation would set out that Rwanda was a safe place to which asylum seekers could be flown. This would allow flights to begin in spring, he said, while declining to guarantee this would happen. While laws can and have been completely passed in as little as a day, there is no special status for emergency legislation, and this can happen only with cross-party support, which seems unlikely in this case. Sunak would, his spokesperson said, urge MPs and peers to back the law because it was what voters wanted. “We believe we are acting to fulfil the wishes of the public, and we are sure that parliament will want to respect that, but obviously they will be able to scrutinise the detail,” he said. Asked what evidence the government could present to show that the public did want the flights to take off, he added: “My belief is that the Rwanda migration partnership remains something that the public wants us to deliver on.” The court ruling dealt a significant blow to the Rwanda plan, which is central to Sunak’s pledge to stop asylum seekers arriving unofficially in the UK in small boats across the Channel, with the intention that people will not make the crossing if they then face deportation, with no prospect of return to the UK. The five judges said there was evidence asylum seekers could face “refoulement” – being sent back to their own countries, where they could face harm, even when they did have a case for asylum. Sunak has also announced a plan to enact a full treaty with Rwanda on how they treat arrivals. It could be published as early as next week. This is also not a rapid process given that there is a delay of at least 21 Commons sitting days before treaties can be ratified. Sunak’s spokesperson said that nonetheless No 10 believed the twin-track of legislation and the treaty “is the fastest route through to getting flights in the air” by trying to close down routes to a legal challenge. Downing Street believes the legislation would close down “systemic” challenges such as judicial reviews, but it remains unclear whether individuals facing deportation could launch court cases. Sunak’s spokesperson said there was confidence No 10 could address the supreme court’s concerns about the safety of asylum seekers in Rwanda. “We’ve done substantive amounts of work in recent months with Rwanda to address some of the concerns raised by the court, whether that’s improving the quality of asylum decision making, ensuring us a stronger judicial oversight of the process,” he said. “We think that the substantive work we have done in preparation for the possibility of this outcome will address the concerns the court raised – obviously the court was looking at a situation from 15 months ago.” It all remains a significant political risk for Sunak, who faces intense pressure from the right of the Conservative party to start deportations. However, the prime minister’s veiled warnings that any intervention from the European court of human rights could prompt the UK to quit the institution have alarmed some centrist Tory MPs. Sunak’s spokesperson said action from overseas courts would cause the government to “revisit international relationships” connected to not just the Strasbourg court but also the UN refugee convention, while giving no further details.