Britain's first scheduled flight taking asylum seekers to Rwanda was due to depart on Tuesday, with the government warning that anyone who avoided it through last-minute legal challenges would be put on a later flight anyway.

Britain has struck a 120mln-pound ($148mln) deal with Rwanda to send some migrants, who had arrived illegally by crossing the Channel in small boats from Europe, to live in the landlocked African country.

The plan has horrified political opponents, charities and church leaders who say it is inhumane. The United Nations' refugee chief called it “catastrophic”, the entire leadership of the Church of England denounced it as an “immoral policy that shames Britain”.

The government says the deportation strategy is needed to stem the flow of migrants risking their lives in Channel crossings and smash the people-smuggling networks.

A government official, who asked not to be named, said there was the possibility after individual legal challenges were heard that the flight could leave with no asylum seekers on it. The government has chartered a private plane, which is scheduled to leave on Tuesday evening.

“We are expecting to send the flight later today,” Foreign Secretary Liz Truss earlier told Sky News. “I can't say exactly how many people will be on the flight. But the really important thing is that we establish the principle.”

“There will be people on this flight and if they're not on this flight, they will be on the next flight because we are determined to break the model of the appalling people traffickers.”

The courts have thrown out last-ditch bids by human rights groups and campaigners to halt the first flight, but London's High Court is set to hear further cases before it departs.

Amid legal challenges, only a few people are now scheduled to leave on the first plane.

Thirty-seven individuals had been scheduled to be removed on Tuesday, which charities said included people fleeing Afghanistan and Syria as well as Iran and Iraq. However, a string of successful legal challenges has reduced that number to seven, according to charity Care4Calais.

At least three High Court appeals were still to be heard.

Human rights groups say the policy will put migrants at risk. The UNHCR has said Rwanda, whose own human rights record is under scrutiny, does not have the capacity to process the claims, and there is a risk some migrants could be returned to countries from which they had fled.

The senior leadership of the Church of England said in a letter to the Times newspaper that those being deported had not had a chance to appeal and no attempt had been made to “understand their predicament”.

A full hearing to determine the legality of the policy as a whole is due in July.

Reuters