The Home Secretary fears next Tuesday’s flight to Kigali will be held up by a High Court injunction after campaigners launched Judicial Review proceedings.
A Home Office insider admitted the chances of it taking off are “slim”. But they added: “There is a chance, albeit a low chance, that it will still happen.”
Campaigners from the Public and Commercial Services Union (PCS), Care4Calais and Detention Action claim plans to send asylum seekers to Rwanda are “unlawful”.
More than 10,000 migrants have crossed the Channel to the UK – mostly in dangerous dinghies – so far this year.
Around 130 are believed to be booked on Tuesday’s flight.
Lawyers for more than 90 of them have submitted legal challenges asking to stay in the UK.
Home Office officials are thought to be anticipating that the remaining 38 will follow suit this week.
Those who have been told they will be sent to Rwanda include a former senior Iranian police officer who fled after giving first-hand testimony of potential human rights violations by the Iranian government. Others say they are unaccompanied minors.
Most of the claims rely on Article 8 of the European Convention on Human Rights – the right to “private and family life” – or involve allegations of modern slavery.
A Tory source said: “It’s no surprise that Labour-supporting organisations and the civil service union are funding legal campaigns to try and cancel the first removal flight.
“They opposed the ending of free movement and now they want to throw open our nation’s borders entirely. They have no alternative to stop the deadly Channel crossings.”
The Independent Chief Inspector of Borders and Immigration David Neal warned that the threat of deporting migrants to Rwanda has not deterred asylum seekers from coming here.
He also criticised the leadership of the Home Office.
He told the Home Affairs Select Committee: “What keeps me awake at night? The fact that Border Force has 10,000 people, immigration enforcement has 4,000 and leadership within those areas could be better.
“The response for the country needs to be better.”
Clare Moseley, the founder of Care4Calais, said the vast majority of people being detained pending their removal to Rwanda are “overwhelmed by total shock and despair”.
She said: “Many came to the UK believing it to be a good place that would treat them more fairly than the places they escaped. We say that the Rwanda plan is unlawful. We hope that the courts will agree.”
Mark Serwotka, general secretary of the PCS union, said: “We are not prepared to countenance our members being put in potentially dangerous and traumatic situations, where they may be asked to act illegally.”
James Wilson, the deputy director of Detention Action, claimed Ms Patel had “overstepped her authority”.
He added: “By rushing through what we say is an unlawful policy, she is turning a blind eye to the many clear dangers and human rights violations that it would inflict on people seeking asylum.”