Migrants being held in detention centres in the UK before they are sent to Rwanda could be tagged and released if legal action means the first deportation flight is delayed.
An urgent bid to block the June 14 flight will be heard at the High Court Friday.
Up to 130 people have been notified they could be removed on the inaugural flight, due to take off on Tuesday but increasingly likely to be delayed. Nine Afghans who fled to the UK after the Taliban takeover are among that number.
Lawyers for more than 90 migrants have already submitted legal challenges asking to stay in the UK, with the rest expected to follow soon.
The charity Care4Calais, the Public and Commercial Services union (PCS) and pressure group Detention Action are seeking a judicial review of the Rwanda scheme — which they have described as “unlawful”.
The PCS union represents more than 80 per cent of Border Force staff.
Asylum Aid is the latest organisation to join the campaign after it said its lawyers had applied on Thursday for an urgent injunction to stop the flight until its judicial review claim could be heard.
The refugee charity, supported by fellow campaign group Freedom From Torture, has asked for the claim to be considered alongside the existing application at Friday’s hearing.
The wave of legal action has cast doubt over whether the first flight will go ahead as planned.
Prime Minister Boris Johnson’s official spokesman said: “We remain confident in our position, should the legal challenges require us going to the courts we will argue our case. It’s true to say the first flight is due for next week so we have that ready to go.”
In the event of a delay, Home Office officials are understood to be prepared to release and monitor those who are being detained with measures which could include placing them on immigration bail and requiring them to sign on regularly at a reporting centre.
The department said it has not ruled out using GPS tagging, although officials confirmed this was not the current policy for the group due to be sent to Rwanda next week.
The government may have to allow the detainees to leave if the flight cannot happen in a reasonable time frame, in line with rules on immigration detention powers which prevent people facing removal being held indefinitely.
Conservative MP Peter Bone called for new legislation allowing deportations to Rwanda to be brought to the House of Commons “immediately” if current plans are stopped in the courts.
Meanwhile, there have been suggestions Zambia is among other countries which have reportedly expressed interest in taking UK asylum seekers, depending on how the Rwanda deal works out.
So far this year 10,020 migrants have crossed the Channel to the UK, analysis of government figures by the PA news agency shows.
The Rwanda policy does not rule out removing Ukrainians and Afghans fleeing conflict if they are deemed by the Home Office to have arrived in the UK illegally — prompting concern from campaigners — as the only nationality exempt from the scheme is Rwandans.
James Wilson, deputy director of Detention Action, said: “In her desire to punish people for seeking asylum by forcing them on to a plane to Rwanda, [Home Secretary] Priti Patel has overstepped her authority.
“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.
“It’s vital that new government policies respect and uphold the laws that we all, as a society, have agreed to follow. That’s why we’re seeking an injunction to keep this plane to Rwanda from leaving the runway.”
Clare Moseley, founder of Care4Calais, said the vast majority of the 100 or so people being detained pending removal to Rwanda that lawyers have spoken to are “overwhelmed by total shock and despair”.
Mark Serwotka, general secretary of the PCS, said: “PCS is not prepared to countenance our members being put in potentially dangerous and traumatic situations, where they may be asked to act illegally.”
Dame Emma Thompson, who has an adopted son from the east African nation, has described the scheme as “eye-wateringly mad and callous” in interview with Sky News’ Beth Rigby, adding that the government’s approach “does not represent the soul of this country”.
Former minister Jesse Norman, who withdrew his long-standing support for Mr Johnson ahead of his confidence vote earlier this week, branded the policy “ugly, likely to be counterproductive and doubtful of legality”.
A Twitter account titled “Our Home Office”, purporting to be run by staff in the department, has been set up expressing its support for refugees amid reports that some civil servants oppose the plan.
It is understood senior Home Office officials are not aware of any staff who have refused to work on the policy.
A Home Office spokeswoman said the department “expected legal challenges, however we are determined to deliver this new partnership”, and that the policy “fully complies with international and national law”.
She added: “Currently all those in scope for the first flight to Rwanda are in detention — we have not ruled out the use of GPS tagging to monitor individuals if they are released from immigration detention.”
At the same time the department announced it had removed 33 foreign criminals, and two people “with no right to be in the UK”, to Albania.