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 Rwanda asylum plan, announced by the government in April, sees some asylum seekers who cross the Channel to the UK given a one-way ticket to Rwanda to claim asylum there instead. The government said the scheme would discourage others from crossing the English Channel.
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 22:30 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 19:30, and triggered a series of legal challenges in London courts. By 22:15 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.