Britain's first flight to take asylum seekers to Rwanda has not taken off as scheduled after the European human rights court issued last-minute injunctions to stop the deportation of the handful of migrants on board.
The British government's plan to send some migrants to the East African country has been criticised by opponents, charities and religious leaders who say it is inhumane, and it has been forced to fight a series of legal challenges in London courts to stop it going ahead.
In the past few days, at least 30 individuals earmarked to be on the first flight successfully argued they should not be deported to Rwanda on health or human rights grounds.
A handful of migrants were set to fly from an air force base in southwest England on Tuesday, but shortly before the plane was due to leave, the European Court of Human Rights (ECHR) granted injunctions to prevent their deportations.
"I have always said this policy will not be easy to deliver and am disappointed that legal challenge and last-minute claims have meant today's flight was unable to depart," Home Secretary Priti Patel said.
"It is very surprising that the European Court of Human Rights has intervened despite repeated earlier success in our domestic courts."
She said the government would not be deterred and would prepare for the next flight.
The ECHR's ruling relating to one of the men, an Iraqi, stated he "should not be removed until the expiry of a period of three weeks following the delivery of the final domestic decision in the ongoing judicial review proceedings".
The High Court in London is due to hold this judicial review in July to decide on the legality of the scheme.
"Last ticket cancelled. NO ONE IS GOING TO RWANDA," the charity Care4Calais, which has launched legal action on behalf of a number of the migrants, said on Twitter.
Britain says the Stg120 million ($A209 million) deal struck with Rwanda will stem the flow of dangerous cross-channel trips and smash the business model of people-smuggling networks.
But the United Nations' refugee chief called it "catastrophic", the entire leadership of the Church of England denounced it as immoral and shameful, and media reports have said Prince Charles had privately described the plan as "appalling".
Prime Minister Boris Johnson, who said his government would not be put off by criticism, had earlier commented that legal bids were undermining attempts to support safe routes for asylum seekers.
Asked if Britain might withdraw from the European Convention on Human Rights, he said: "It is certainly the case that ... the legal world is very good at picking up ways of trying to stop the government from upholding what we think is a sensible law.
"Will it be necessary to change some laws to help us as we go along? It may very well be and all these options are under constant review."
Shah said Britain would join Belarus and Russia in not being part of the convention if it did opt out.