Asylum seekers will be flown for processing in Rwanda under government plans expected to be announced as ministers face pressure to tackle small boat crossings of the Channel.
But ITV News has seen a government document that raises issues over the legality of such a policy.
The government document says the policy would carry the risk of legal challenges but is possible under current legislation should the government wish to push ahead.
Boris Johnson is set to argue on Thursday that action is needed to combat the “vile people smugglers” turning the ocean into a “watery graveyard”.
The document seen by ITV News also states that any agreement of this nature would require the government to financially incentivise whichever country it reaches a deal with. Initial estimates had the policy costing in the tens of millions, but the document says this has been revised to the hundreds of millions.
ITV News Political Correspondent Libby Wiener outlines the proposed plans
Similar policies have been considered in other nations like Denmark, while Australia already has policy in place whereby asylum seekers are sent to Christmas Island for processing.
The document questions the success of these schemes, saying the evidence of effectiveness is mixed.
The Home Office has dismissed these concerns, suggesting the document is now out of date and insists that the Australian model had been successful in reducing illegal journeys and dismantling people smuggling networks.
A Home Office spokesperson added: “The over £1bn a year cost of the broken asylum system, including accommodating asylum seekers in hotels, is unsustainable.
“We’ve always been clear that we are committed to working closely with a range of international partners to fix our broken asylum system and reduce the pull factors to the UK.
“Our New Plan for Immigration will ensure a firm but fair system, helping those in genuine need while tackling people smuggling gangs.”
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ITV News understands that talks with Rwanda over the partnership had been going on for some months before plans for the announcement were finalised.
The PM, who will also be speaking on Thursday, has been under pressure after being fined for breaching coronavirus laws. He will argue the nation voted to “control” immigration in the Brexit referendum rather than control borders, and that “our compassion may be infinite, but our capacity to help people is not”.
“So just as Brexit allowed us to take back control of legal immigration by replacing free movement with our points-based system, we are also taking back control of illegal immigration, with a long-term plan for asylum in this country,” he is expected to say.
“It is a plan that will ensure the UK has a world-leading asylum offer, providing generous protection to those directly fleeing the worst of humanity, by settling thousands of people every year through safe and legal routes.”
Many details of the expected announcement, such as whether it would apply just to those who arrived by what the government calls illegal means, remained unclear.
Charities have warned the “cruel and nasty decision” to “offshore” some asylum seekers more than 6,000 miles away will fail to address the issue, “lead to more human suffering and chaos” while potentially costing millions.
British Red Cross executive director Zoe Abrams said the humanitarian network was “profoundly concerned” about the plans to “send traumatised people halfway round the world to Rwanda”.
“The financial and human cost will be considerable...We are not convinced this drastic measure will deter desperate people from attempting to cross the Channel either. People come here for reasons we can all understand, like wanting to be reunited with loved ones, or because they speak the language. Making it harsher may do little to stop them risking their lives,” she said.