A flight that was due to take asylum seekers from the UK to Rwanda was cancelled minutes before take-off following a late legal challenge.
The UK government says it will arrange another flight to the African country, and insists the scheme will discourage people from crossing the English Channel.
What is the Rwanda asylum plan?
The five-year trial will send some refugees to Rwanda, to claim asylum there.
They may be granted permanent refugee status to stay in Rwanda. If not, they can apply to settle there on other grounds, or seek asylum in a "safe third country".
The policy is aimed at people who arrive in the UK through what the government calls "illegal, dangerous or unnecessary methods", such as on small boats or hidden in lorries, when they could have claimed asylum in another safe country - such as France.
How many people could be sent to Rwanda?
"Anyone entering the UK illegally" after 1 January could be sent, with no limit on numbers, UK prime minister Boris Johnson said.
Originally 37 people were due to be on the Tuesday flight, but legal challenges had already reduced that number to about seven before it was cancelled.
Under the deal, Rwanda can also ask the UK to take in some of its most vulnerable refugees. Rwanda says this will only be a few "outlier" cases.
What are the legal challenges?
Charities and lawyers representing asylum seekers had launched a series of legal challenges against the policy.
Critics questioned whether Rwanda is a safe destination, and argue that the scheme breaks the European Convention on Human Rights.
As a result, some individuals had already been removed from the flight. But a final attempt to block it altogether was rejected by the Court of Appeal on Monday and upheld by the Supreme Court on Tuesday.
However the flight was halted after a late intervention from the European Court of Human Rights (ECtHR). This isn't an EU body but is part of the Council of Europe, which still counts the UK as a member.
It ruled that an Iraqi man known as KN faced "a real risk of irreversible harm" if he was sent to Rwanda.
The judgment triggered further legal challenges, and all passengers were eventually removed.
Home Secretary Priti Patel said she was "disappointed", but added, "preparation for the next flight begins now".
The Supreme Court is due to hold a judicial review into the policy in July. If it says it is unlawful, any sylum seekers sent to Rwanda could be returned.
An opinion poll carried out on Monday suggests the the scheme is divisive.
Of the 2,463 people surveyed, 44% backed the policy - including 27% who "strongly" supported it. Meanwhile, 40% were against it, including 28% who were "strongly" opposed.
How much will it cost?
The government says the asylum system costs £1.5bn a year, with more than £4.7m a day spent on hotels to accommodate homeless migrants. Critics say the daily cost is so high because the Home Office backlogs are at a 10-year high - it's taking too long to decide on applications - and asylum seekers are banned from working until they get the green light to do so.
That massive daily hotel bill also covers the costs of housing thousands of Afghans the UK rescued last year as the Taliban advanced.
Home Office Minister Tom Pursglove said a £120m upfront payment to Rwanda would be followed by further payments as the country handled more cases.
He said the cost would be "similar to the amount of money we are spending on this currently", and that "longer term, by getting this under control, it should help us to save money".
But officials in the Home Office are publicly sceptical. The top civil servant warned the Home Secretary in a formal letter that there was a lack of evidence to demonstrate that the policy would have enough of a deterrent effect to be value for money.
Comparisons have been made to Australia's offshore processing system, which was estimated to cost $957m (£546m) in 2021-22.
Liz Truss declined to confirm what the Tuesday flight would cost. However, removing people from the UK by charter flight cost more than £13,000 per person in 2020.
What's life like in Rwanda?
Reports say Rwanda has adapted basic hostels near the capital Kigali to house migrants from the UK.
Rwanda's government says it is ready to handle 1,000 asylum seekers from the UK during the trial, but has capacity for many more. The UN's refugee agency is sceptical - saying that it has concerns the country can't manage arrivals from the UK because it has too few lawyers, case workers and interpreters to deal with them.
Government spokesperson Yolande Makolo said: "We want Rwanda to be a welcoming place and we will do our best to make sure that the migrants are taken care of, and that they are able to build their lives here."
Rwanda is already home to around 150,000 refugees from other African countries, including neighbouring Burundi and DR Congo. It also hosts migrants who tried to cross the Mediterranean to Europe via Libya.
Some refugees work as farm labourers and domestic servants. Most are unemployed, relying on state benefits of about £35 a month.
Rwanda's government says the country has undergone a development "miracle" since 1994, when a genocidal war killed 800,000 people.
However, about 70% of the country's 13 million people are subsistence farmers, meaning they eat, rather than sell, what they grow.
Is the scheme stopping people from crossing?
The Rwanda policy was first announced by the UK government on 14 April.
Between 18 April and 5 June, 3,599 asylum seekers are known to have arrived in small boats.
Although this is less than the 4,554 people who arrived between April and June 2021, the total is likely to increase when figures for the whole April to June period become available.
In the whole of 2021, 28,526 people are known to have crossed in small boats - up from 8,404 in 2020. The total figure this year is set to be much higher than last year, according to Border Force union officials. It is likely they will be lower than the records seen during Tony Blair's time as prime minister - and still far lower than the numbers seeking asylum in France and Germany.
In 2021, 75% of arrivals were men aged 18 to 39. About 5% were men aged over 40, 7% were women over 18, and 12% were children under 18 (of whom three-quarters were male).
Previously, Iranians made up the vast majority of arrivals - 80% in 2018, and 66% in 2019.
Recently, there has been a greater mix of nationalities making the crossing. Iranians made up 30% of small boat arrivals last year, while 21% were Iraqis, 11% Eritreans and 9% Syrians, according to the Home Office.