The first asylum seekers could be shipped off to Rwanda within "weeks", amid reports the policy was pushed through by the Home Secretary despite concern from senior aides.
Home Secretary Priti Patel says her "world-class" plan to send migrants to Rwanda will act as a "blueprint" for other countries to follow, despite reports of a civil service backlash over the plan.
Ms Patel has claimed her million pound deal could be reproduced by other countries in Europe, such as Denmark.
The plan - which will see asylum seekers flown 6,000 miles away to east Africa - has been heavily criticised by charities and opposition parties as being "shamefully cruel".
The UN refugee agency has claimed Ms Patel's plans are a breach of international law, while a peer has suggested that the proposals for processing may breach the Geneva convention.
Reports claim that Ms Patel issued a "ministerial direction" in relation to the Rwanda asylum plan, overruling concerns from her own civil servants.
Ministerial directions are used when the top civil servant in a department has objected to the costs or feasibility of a spending plan.
Multiple reports have surfaced that Ms Patel took the rare step of issuing a ministerial direction to overrule concerns of one of her top civil servants about whether the concept will deliver value for money.
The claimed use of the ministerial direction by the Home Secretary was only the second deployment of the power within the Home Office in the past 30 years, according to the Daily Telegraph.
The Home Office declined to comment.
The Telegraph said unions representing staff in Whitehall have warned of mass walk-outs and transfer requests over ethical and legal concerns about the policy, claiming Ms Patel faces a "mutiny" over her recently unveiled concept.
It comes as the Ministry of Defence confirmed 181 migrants crossed to the UK on six boats on Good Friday, with more expected during the good weather over the Easter weekend.
The Royal Navy took over "operational command" of handling migrants crossing the Channel on Thursday.
About 6,000 people have been brought ashore after crossing the English Channel in small boats so far this year.
Andrew Griffith, the director of policy at Downing Street, said it is hoped the Rwanda scheme will be operational in “weeks, or a small number of months”, as concerns over illegal crossings continue.
Asked when he expects the first migrant will be sent to Rwanda, the Conservative MP told BBC Newsnight: “It doesn’t require new legislation – we think that we can do this under the existing conventions.
“And therefore this should be possible to be implemented and operationalised in weeks, or a small number of months. So we are ready to go in that sense.”
Speaking to LBC's Andrew Castle, prisons minister Ellie Reeves said the proposals are "completely the wrong policy".
"It's costly and it does nothing to target the criminal gangs," Ms Reeves said.
She claimed the Home Office is in "disarray", citing the Homes for Ukraine Refugee scheme, which has been slammed for being too slow at processing visas for those fleeing the warzone.
"We need to speed up our asylum process," she told Andrew.
"We've got a Home Office in disarray, we've seen that with the queues and delays at the border over recent weeks, we've seen that with delays sorting out the Homes For Ukraine visas."
She said we need to be targeting criminal gangs and must have a closer cooperation with France to tackle illegal crossings.
Charities and opposition parties have branded Ms Patel's plans"evil" and "despicable" as critics blasted the PM's announcement, saying it simply "will not work".
Enver Solomon, chief executive of the Refugee Council charity, said the Government's plan to process asylum seekers in Rwanda are unworkable.
"I think it's rather extraordinary that the Government is obsessing with control instead of focusing on competence and compassion, creating the asylum system," he said.
"We stick to the principles that every prime minister since Winston Churchill has always stuck to, that you grant people a fair hearing on UK soil.
"There's no reason why we shouldn't do that today because that is the principle that the UN Convention, which we were one of the founding signatories of, enshrines.
"This proposal that Government is putting forward just simply isn't going to work."
Both Mr Johnson and Ms Patel have acknowledged the plans could be challenged in the courts.
Defending the plan, justice and immigration minister Tom Pursglove told broadcasters that there was a "moral imperative" to crush the "cruel" business model of human traffickers making money out of migrants wanting to cross the Channel.
He also argued the scheme would save taxpayers money in the "longer-term", although he accepted the short-term cost would be equivalent to what the UK currently pays to accommodate and process asylum seekers domestically - approximately £5 million per day.
The revelations have seen over 160 campaign groups sign an open letter to the Prime Minister and Home Secretary Priti Patel, demanding that the Government scrap the scheme, cease plans to overhaul the Human Rights Act, and "instead create humane and effective solutions" for those seeking refuge in the UK.
"Sending people seeking asylum to Rwanda will cause immense suffering, with the most vulnerable people bearing the brunt," they wrote.
"This is a shamefully cruel way to treat people who have come to the UK to seek protection, fleeing persecution or conflict."
They said to send people seeking asylum to Rwanda would be "cruel and immoral", criticising the country's track record on human rights.
The Prime Minister said the partnership would be "fully compliant with our international legal obligations", while insisting Rwanda is "one of the safest countries in the world" and is "globally recognised for its record of welcoming and integrating migrants".
Speaking to reporters, Ms Patel argued the plan was likely to be emulated by others, including countries in Europe.
"There is no question now that the model we have put forward, I'm convinced is world class and a world first, and it will be used as a blueprint going forward, there's no doubt about that," Ms Patel said.
"I would not be surprised if other countries start coming to us direct on the back of this as well."
The Home Secretary said Copenhagen was in talks with Rwanda as well, adding the Council of Europe "have also basically said they are interested in working with us".