Anger is mounting after it emerged the UK government was told by one of its own advisers that Rwanda tortures and kills political opponents - but continued with plans to send refugees there anyway.
An email disclosed to the High Court said "arbitrary detention, torture and even killings are accepted methods of enforcing control too".
Both candidates hoping to become the next Prime Minister have vowed to continue with the scheme, which has been branded "unworkable" and "unethical" by critics.
The government is attempting to keep parts of documents about the project - which has already cost taxpayers at least £120 million - secret, citing national security concerns.
The controversial policy, was announced earlier this year by Home Secretary Priti Patel, and it has emerged that in an email sent on April 26 - two weeks after the unveiling - a government insider raised concerns about the way Rwanda's human rights record was being presented.
The email read: “There are state control, security, surveillance structures from the national level down to [households]. Political opposition is not tolerated and arbitrary detention, torture and even killings are accepted methods of enforcing control too.”
A legal challenge over government attempts to keep more comments out of the public eye is ongoing.
After the email came to light, Labour's shadow Home Secretary Yvette Cooper MP said: “This is further evidence that the Home Office overruled clear advice from officials about serious problems with the Rwanda scheme, and it is deeply concerning that they are now attempting to conceal the truth from the public.
“Nothing about this unworkable Rwanda deal has been transparent. They have tried to hide grave concerns about torture and abuse as well as hiding the total cost to the taxpayer which is likely to be in the hundreds of millions."
She said that her party has a serious plan to tackle Channel crossings, proposing a new cell to crack down on criminal gangs.
Ms Cooper added: "At the moment we have government by gimmick when people's lives are at risk and it is unacceptable.”
In a rare moment of party disunity, Rishi Sunak was last night told by an audience member at the Tory leadership hustings in Perth that the policy was "inhumane".
The party member urged him to negotiate a better solution to small boat crossings with the French.
He disagreed, adding: "Making the Rwanda policy work is an important part of getting a grip of this situation."
Asked if he knew about warnings to ministers that Rwanda would kill political opponents sent there, Mr Sunak said: "The United Nations believed that Rwanda is fine so I do think it is fine to do it."
Steve Crawshaw, director of policy and advocacy at Freedom from Torture said: “It is deeply disturbing that UK ministers have once again ignored warnings about the use of torture and arbitrary killings by the Rwandan state, particularly given that torture survivors were among those that this government attempted to send to Rwanda in June."
He continued: "Instead of pursuing these dangerous ‘cash-for-humans’ schemes, the government should expand safe routes to protection, strengthen international cooperation on refugee protection and ensure diplomatic and humanitarian interventions to reduce push factors driving people to make perilous journeys to reach safety.”
Several asylum seekers, the Public and Commercial Services union (PCS) and charities Care4Calais, Detention Action and Asylum Aid are challenging the Home Office over proposals to provide one-way tickets to the east African country.
Ahead of the main hearing in the challenge due in September, the Home Office has brought a bid to keep about 10 extracts from two documents secret, including from the lawyers for the asylum seekers, and charities and the union.
The court heard that the Home Office had asked for someone in the Foreign, Commonwealth and Development Office (FCDO) with knowledge of the region to review their Country Policy and Information Note for Rwanda - a document produced to summarise conditions in the country.
The Home Office is claiming public interest immunity on parts of the independent reviewer's response, in an email and comments added to the draft, preventing them from being shared.
Neil Sheldon QC, for the department, told the court that there would be a "potential of very significant harm" to international relations and national security issues if the extracts were disclosed.
In written submissions, Mr Sheldon said that the redacted material "comprises expressions of opinion, of a general nature", adding: "The commentary it contains amounts to nothing more or less than the un-referenced opinion of this particular individual."
However, Christopher Knight, representing eight individuals, PCS, Detention Action and Care4Calais, opposed the bid, along with other claimants and three media organisations.
Mr Knight said it was important for the court to decide whether the redactions "go materially beyond or differ from the public criticisms made" about the Rwandan government by the UK.
Foreign Office minister Graham Stuart said that disclosing the full documents would cause serious harm "primarily but not exclusively" to the UK's relationship with the Rwandan government.
He added that sharing the contents of the extracts would also harm national security "in light of Rwanda's status as a valuable strategic partner to the United Kingdom across a range of issues including regional security, the maintenance of a strong coalition in support of Ukraine and combating the activities of criminal gangs engaged in illegal immigration".
A Government spokesperson said: “Rwanda is a safe and secure country with a track record of supporting asylum seekers.
“We remain committed to delivering this policy to break the business model of criminal gangs and save lives.”
