The UN’s refugee agency has condemned Boris Johnson’s plan to send asylum seekers to Rwanda as “a symbolic gesture” that will be unworkable in practice. Speaking to the Guardian, Gillian Triggs, the assistant high commissioner at the UNHCR, said the proposed arrangement would only accommodate a few hundred people a year, making it extremely expensive as well as illegal and discriminatory. Ministers insisted on Friday that the scheme would save money in the “longer term”, despite a reported cost of up to £30,000 per person. But government insiders said the expected torrent of legal battles could leave it costing substantially more, with some predicting it could take two years before anyone was flown to Rwanda. Home Office sources said they were braced for judicial reviews and a wave of immigration tribunals over the lawfulness of attempts to offshore asylum seekers who arrive after travelling across the Channel on small boats. There are two appeal stages for judicial reviews and three for those seeking to challenge their removal through an immigration tribunal, casting in more doubt Johnson’s stated aim of removing people to the central African country in the next six weeks. Home secretary Priti Patel signed a “ministerial direction” authorising the policy to be implemented despite an objection on spending grounds from her department’s permanent secretary. A Home Office source said the ministerial direction was issued because the savings made in the long-term by the new policy could “not be quantified with certainty” but that Patel did not want to let “a lack of precise modelling” hold the decision back. Downing Street has said it expects that thousands of asylum seekers will be relocated within the first few years of the scheme. Triggs accused the UK of “attempting to shift its burden to a developing country” and warned that the arrangement signed off by Patel “would not comply with the UK’s international legal responsibilities”, adding: “All the indications are that it will be unworkable.” Triggs continued: “We want to end the vulnerability of people on the move to people-trafficking and of course we want to stop people drowning, but we strongly disagree with victimising the very people who need protection. There should instead be an increase in legal pathways to the UK.” The proposals seemed designed to appeal to anti-migrant sentiment in the UK, she suggested. “We are a politically neutral, humanitarian body – it’s not really for me to comment on the politics,” Triggs said. “But we are in an environment in which populist governments will appeal to their rightwing, anti-migrant sentiment and this would presumably be part of that.” Two former Tory international development secretaries on Friday voiced their opposition to the policy, and cast doubt on whether the government would successfully fly anyone to Rwanda. Rory Stewart told the Guardian there was a “very strong possibility it’s complete pie in the sky” and had been “rushed out to distract people” from the prime minister being fined by police for attending a party in Downing Street that broke Covid laws. Stewart, a minister under Theresa May, said that when he was in government, it was hard enough to remove citizens of some countries back to their place of birth. “It’s a completely extraordinary thing to be doing and I think legal challenges will mean they won’t make it on to the planes,” he predicted. Stewart, who visited Rwanda earlier in the month, said it was “one of the very poorest countries on Earth” and a “particularly extreme environment into which to put people”. The Conservative MP Andrew Mitchell also said it was an impractical, immoral and incredibly expensive plan. “The costs are eye-watering,” he told the BBC. “You’re going to send people 6,000 miles into central Africa – it looked when it was discussed in parliament before that it would actually be cheaper to put each asylum seeker in the Ritz hotel in London.” Triggs also warned that the UK was introducing a discriminatory approach towards refugees, offering an uncapped scheme for asylum seekers from Ukraine and a “draconian” system for refugees from other countries. “At the political level, we are seeing levels of discrimination,” Triggs said. “We are deeply concerned that the processes appear to be discriminatory. One of the fundamental principles of international law is is non-discrimination on the grounds of race or ethnicity or nationality.” Triggs hoped the popular support for Britons to house Ukrainian refugees would encourage the government to rethink its proposals. She said: “We saw an outpouring of sympathy and generosity by the British people themselves. So we see this announcement as out of character with British values. We hope that the public response will help to ameliorate the negative aspects of this proposal with Rwanda.” Johnson was also sent a letter by 150 British organisations supporting refugees that warned the plan would “cause immense suffering” and “result in more, not fewer, dangerous journeys – leaving more people at risk of being trafficked”. The signatories, including the Joint Council for the Welfare of Immigrants, LGBT+ refugee advocates Rainbow Migration and HOPE not Hate, said Rwanda had “a poor record on human rights” and the most vulnerable people were set to “bear the brunt”. Alf Dubs, a Labour peer who was a child refugee, told the Guardian he expected there would be “quite a battle” over the issue. The Bishop of Durham, who also sits in the House of Lords, has signalled his opposition to the policy, saying it is “wrong in so many ways”. Home Office minister Tom Pursglove defended the Rwanda initiative, saying it would “crush” the business model of people smugglers and lower the costs of housing all those that arrive in the UK illegally, which he said ran to £5m per day. He said on top of the £120m already committed to fund the scheme, “we will continue to make contributions to Rwanda as they process the cases, in a manner that is similar to the amount of money we are spending on this currently here in the UK”. Pursglove added: “But longer term, by getting this under control, it should help us to save money. “We are spending £5m per day accommodating individuals who are crossing in hotels. That is not sustainable and is not acceptable and we have to get that under control.”