Rwanda plan not certain to deter migrants, says official

Priti Patel's top civil servant warned her there was not enough evidence of the "deterrent effect" of the plan to send some asylum seekers to Rwanda.

In a letter, Matthew Rycroft said the policy would only be value for money if it stopped illegal Channel crossings.

But the home secretary replied it would be "imprudent" to allow a lack of modelling to delay the scheme.

The letters were released after Ms Patel had to personally approve the scheme amid officials' concerns.

The exchange between Ms Patel and her permanent secretary was published by the Home Office after it emerged she had issued a rare "ministerial direction" to push through the plans, meaning she takes responsibility for it.

Under the £120m scheme - which was announced this week - people deemed to have entered the UK unlawfully will be transported to the east African country, where they will be allowed to apply for the right to settle.

It has faced widespread opposition, with more than 160 charities and campaign groups urging ministers to scrap what they described as a "cruel" policy. It has also been criticised by opposition parties and some Conservatives.

In a letter to the home secretary dated 13 April last year, Mr Rycroft said she had made it clear the "rationale" for the policy was to "break the business model of people smugglers, while maintaining a fair and robust immigration and borders system".

He acknowledged it was also to prevent the "tragic loss of life in the Channel", deter "hazardous and illegal journeys to the UK" and to tackle the £1.5bn per year cost of the asylum system to the British taxpayer.

The permanent secretary said while it was "regular, proper and feasible for this policy to proceed" there was "uncertainty" over whether the plan would be value for money.

He said there were "potentially significant savings to be realised from deterring people entering the UK illegally" but the scheme's value for money depended on how well it deterred people from making those journeys.

He wrote: "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."

"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 said this didn't mean that the scheme could not provide a deterrent - but said there was "not sufficient evidence for me to conclude that it will."

In her response dated the same day, Ms Patel said she understood it was not possible for the government to accurately model the scheme's deterrent effect "from day one" but said she was "confident this policy is our best chance at producing that effect".

She said: "without action, costs will continue to rise, lives will continue to be lost."

The home secretary added it would be "imprudent" to "allow the absence of quantifiable and dynamic modelling - which is inevitable when developing a response to global crises influenced by so many geopolitical factors such as climate change, war and conflict - to delay delivery of a policy that we believe will reduce illegal migration, save lives, and ultimately break the business model of the smuggling gangs".

Ms Patel formally directed Mr Rycroft to proceed with the scheme with immediate effect.

Here's what we know about the scheme so far: