It has now emerged Priti Patel was warned about the Rwanda plan by a top civil servant just the day before the scheme was unveiled.
Under the £120m plan, any refugee found to be entering the UK illegally will be flown 4,000 miles to Rwanda where they can apply to stay to rebuild their lives.
The proposal has sparked a furious reaction from MPs from both parties, refugee charities and human rights lawyers. The Archbishop of Canterbury Justin Welby used his Easter sermon to say “it was the opposite of the nature of God”.
Now it has now come to light Matthew Rycroft had warned Ms Patel about the “uncertainty” over “value for money” in a letter to her dated on Wednesday, just one day before the announcement.
The Permanent Under-Secretary of State at the Home Office said there was not “sufficient evidence” to conclude at present that the policy would put migrants off travelling to the UK.
“Evidence of a deterrent effect is highly uncertain and cannot be quantified with sufficient certainty to provide me with the necessary level of assurance over value for money.” He wrote.
“I do not believe sufficient evidence can be obtained to demonstrate that the policy will have a deterrent effect significant enough to make the policy value for money.”
Mr Rycroft also said he recognised the scale of the issue and that it was “regular, proper and feasible for this policy to proceed”.
In a letter dated the same day, the Home Secretary responded saying she was “confident this policy is our best chance” at a deterrent effect.
She wrote: “It is not possible for HMG to accurately model the deterrent effect from day one.”
The Home Secretary went on: “Without action, costs will continue to rise, lives will continue to be lost.”
Ms Patel formally instructed Mr Rycroft to proceed with the scheme.
The Home Office has published the exchange after it emerged the Home Secretary used a rare ministerial decison to go ahead with the plan which have sparked controversy.
More than 6,000 people have crossed the Channel since the start of the year compared to 28,526 the year before, according to the Home Office.
A Home Office spokesperson said: “The UK has a proud history of supporting those in need of protection and our resettlement programmes have provided safe and legal routes to better futures for hundreds of thousands of people across the globe.
“However, the world is facing a global migration crisis on an unprecedented scale and change is needed to prevent vile people smugglers putting people’s lives at risk and to fix the broken global asylum system.
“Rwanda is a fundamentally safe and secure country with a track record of supporting asylum seekers. Under this agreement, they will process claims in accordance with the UN Refugee Convention, national and international human rights laws.”