The first flight due to take asylum seekers from the UK to Rwanda was cancelled minutes before take-off after legal rulings on Tuesday evening.
Up to seven people had been expected to be removed to the east African country.
But the flight was stopped after a late intervention from the European Court of Human Rights (ECtHR) led to fresh challenges in the UK courts.
Home Secretary Priti Patel said she was “disappointed” but added: “Preparation for the next flight begins now.”
However, James Wilson from campaign group Detention Action said the rare intervention from the ECtHR “shows how potentially dangerous” the Rwanda removals are.
He said the court had recognised no one should be forced on to a plane until the policy was fully scrutinised in a High Court hearing next month.
The cancellation of the flight followed days of arguments in UK courts, ending with the home secretary getting the go-ahead to begin transporting some of the asylum seekers.
A Boeing 767, chartered at an estimated cost of £500 000, had been due to take off at 10:30 p.m. BST from a military airport in Wiltshire.
But a judgement from the ECtHR in Strasbourg halting the deportation of one of the men arrived just after 7:30 p.m., and triggered a series of legal challenges in London courts. By 10:15 p.m., all the passengers had been removed from the plane, which then returned to Spain.
The Strasbourg human rights court – part of the Council of Europe, which still counts the UK as a member, rather than the European Union – said an Iraqi man known as KN faced “a real risk of irreversible harm” if he remained on the flight.
Whereas the High Court in London had found that KN could be returned to the UK if his bid to overturn the Rwanda transportation policy succeeded, the ECtHR said there was no legally enforceable mechanism to ensure he could come back from east Africa.
The Strasbourg court also said the UN had raised concerns that UK asylum seekers transferred to Rwanda would not have access to “fair and efficient” procedures to determine their refugee status.
And it noted that the High Court had acknowledged there were serious issues regarding whether Rwanda had been correctly assessed as a safe third country.
The home secretary said these “repeated legal barriers” were similar to those the government faced on other deportations, adding that “many of those removed from this flight will be placed on the next”.
Ms Patel said that she had always maintained this policy would “not be easy to deliver” but added it was “very surprising” the European court had intervened after the government had been permitted to go ahead with the flights by domestic courts.
“Our legal team are reviewing every decision made on this flight and preparation for the next flight begins now,” she said.
The Rwandan government said it remained committed to its deal with the UK and was “not deterred” by the failure of the first flight to depart.
Spokeswoman Yolande Makolo said: “Rwanda stands ready to receive the migrants when they do arrive and offer them safety and opportunity in our country.” (BBC)
