Legal action is being brought against the policy announced by outgoing Home Secretary Priti Patel by several asylum seekers, along with the Public and Commercial Services union (PCS) and charities Care4Calais and Detention Action.
Ms Patel announced the “world-first” agreement with Rwanda agreement in April in a bid to deter migrants from crossing the Channel by providing one-way tickets to some asylum seekers.
On Tuesday, UNHCR – the UN Refugee Agency – told the court that Rwanda “lacks irreducible minimum components of an accessible, reliable, fair and efficient asylum system”.
“There are serious defects in the Rwandan refugee status determination system,” said Laura Dubinsky QC, for UNHCR.
“There can be no realistic prospect of improvement where defects are not recognised but denied by the government of Rwanda,” she added.
UK minister says Britain will push ahead with migrant deportations to Rwanda - video
Ms Dubinsky later said in written submissions that the policy was a “burden-shifting arrangement” that would lead to a serious risk of refoulement – that people would be expelled or returned to a country where their life and safety might be in danger – and that it goes against the Refugee Convention’s prohibition against penalising refugees for entering a country illegally.
“UNHCR regrets, particularly in relation to one of the founding states of the Refugee Convention, that it is necessary for it to warn that the UK-Rwanda Arrangement is incompatible with UK’s fundamental obligations under the Refugee Convention,” The barrister concluded.
Judges previously heard that UNHCR has been in Rwanda since May 1993, with more than 300 people working in the country as of June this year.
In written submissions, Ms Dubinsky said that Home Office officials “have acknowledged, internally, their lack of any other independent verification concerning the position on the ground in Rwanda”.
The barrister later argued that some asylum claims are improperly rejected by the Rwandan Directorate-General of Immigration and Emigration (DGIE) without proper consideration, “effectively hidden from view”.
“The fact that a part of the Rwandan asylum system sometimes operates outside of Rwandan law… significantly increases the risk of arbitrary decision making,” she said.
Inside a refugee camp in Rwanda - video
The court heard that the government of Rwanda denies that the DGIE makes these decisions.
In written submissions, lawyers for the asylum seekers and charities said that UNHCR had raised concerns with Home Office officials in March over the treatment of asylum seekers from the Middle East or who are LGBT.
They said UNHCR reported that asylum-seekers from the Middle East were “systematically rejected in their claims” for asylum in Rwanda with a 100 per cent refusal rate for Afghan, Syrian and Yemeni people.
Raza Husain QC, for some of the individuals, the charities and the union, added that the UN agency had “consistently received reports that LGBTQ+ asylum seekers are not able to register their claims based on their sexual orientation or gender identity because their claims are verbally rejected”.
The court heard that the government of Rwanda denies refusing access to LGBT asylum seekers, calling the allegation “demonstrably untrue”.
The Home Office is defending the claims, with lawyers arguing the memorandum of understanding agreed between the UK and Rwanda provides assurances that ensure everyone sent there will have a “safe and effective” refugee status determination procedure.
The Home Office legal team, which includes Lord Pannick QC and Sir James Eadie QC, also argued there is no risk of those who are not granted refugee status in Rwanda being removed to their country of origin.
“All the individual claimants who have received removal directions for removal to Rwanda have been pre-approved by Rwanda for the purposes of processing their asylum claims," they said in written submissions.
“There is no risk of them being refused entry.”
UK's first Rwanda deportation flight cancelled - video
The barristers, who are due to begin their oral arguments on Wednesday, added: “Rwanda does not conduct forcible removals to the countries of which these claimants are nationals.”
The government’s lawyers added there was no risk of indirect refoulement as “the only country they could be returned to is the UK”.
They added the UK’s agreement with Rwanda provided “assurances” on “concerns” over with the east African country’s refugee status determination procedure raised by UNHCR.
The hearing is due to last for five days, with a second hearing in a claim brought by the group Asylum Aid taking place in October.
Decisions on both sets of claims are expected to be given in writing at the same time.