Home Office staff are aware that they cannot detain people indefinitely if they are not sent to the east African country in the first planned flight. An emergency high court hearing that challenges Priti Patel’s policy is to be held at 10.30am on Friday. It will determine whether the first flight can go ahead on Tuesday as scheduled. Government sources confirmed there was a “healthy chance” that Friday’s challenge would be successful, causing the chartered flight to be postponed. If that happens, officials are understood to be prepared to release and tag those currently detained. Decisions would be made after taking into consideration the Hardial Singh principles, which reference a legal precedent that sets limits on the Home Office’s immigration detention powers. Friday’s hearing comes after a judicial review was launched on Wednesday by the Public and Commercial Services Union (PCS), the charity Care4Calais and the pressure group Detention Action, along with four asylum seekers facing removal to Rwanda. The case will challenge aspects of the policy, which was unveiled by Boris Johnson, including Patel’s right to carry out such removals, the rationality of Patel’s claim that Rwanda is generally a “safe third country”, the adequacy of provision for malaria prevention in Rwanda, and whether it complies with the Human Rights Act. Also, officials are refusing to rule out sending Afghans to Rwanda on Tuesday, despite the deteriorating political situation in their home country. The only nationality of people who will not be considered for the new policy are Rwandans themselves. Existing government schemes to assist refugees from Afghanistan – the Afghan relocations and assistance policy, launched in April 2021, and the Afghan citizens resettlement scheme – have proved difficult to access, MPs have been told. It was also reported on Wednesday that Zambia may be the next country to take UK asylum seekers. The Home Office is refusing to say how many people it plans to send to Rwanda on Tuesday, or how many people have been sent letters of intent for other possible flights. Officials have refused to deny claims that 130 people could be removed next week, but the Guardian has been told the number is around 30. The Home Office has been approached for comment.