Assurances from Priti Patel about the Government’s controversial Rwanda scheme failed to satisfy a custody deaths watchdog, which is preparing to write to the next home secretary with “outstanding concerns”.

With Liz Truss widely tipped to emerge as the winner of the Tory leadership contest, it is expected that she could replace Priti Patel as Home Secretary after becoming prime minister on Tuesday.

In the in-tray of any new secretary of state will be a letter from the Independent Advisory Panel on Deaths in Custody (IAPDC), which advises the Government on how to prevent deaths in custody, was left with concerns and several unanswered questions after an exchange of letters with Ms Patel during the summer.

Ms Patel earlier this year signed what she described as a “world-first agreement” with Rwanda in a bid to deter migrants from crossing the Channel.

But the first deportation flight, due to take off on June 14, was grounded amid legal challenges.

Among those questions the expert panel deemed unanswered were how people might be screened for declining physical and mental health and whether a risk of suicide and self-harm will be taken into account by UK authorities.

In a letter sent to the Home Secretary on June 10, the watchdog’s chairwoman Juliet Lyon set out a number of questions about how the Government plans protect detained asylum seekers.

The questions asked about plans for holding people safely during the period of arrival in the UK to arrival in Rwanda and on how mental and physical health needs will be assessed during the process.

“Will some form of assessment be used to determine which detainees are selected for processing in Rwanda and which in the UK? If so, will this assessment take account of health and vulnerability?

“Will people be screened for deteriorating serious physical and mental health conditions?

“Will risk of suicide and self-harm be assessed and what steps will be taken to mitigate this risk?

“Will detainees have the opportunity to establish and maintain contact with their families?

“Is it proposed that accountability for safety will be transferred from UK government to that of Rwanda?

“If so, at what stage during the period referred to as ‘processing’ will this occur and what steps will be taken to ensure that these important responsibilities continue to be carried and human rights obligations met?”

The panel also pressed the Home Secretary for answers on the specific role of the army, immigration enforcement, Border Force and other organisations in the Rwanda scheme, while also asking if specific arrangements have been made for interpreters.

In a response dated July 22, Ms Patel said that all those detained will have access to independent interpreting services, while also confirming that individuals will have “various means for maintaining contact with friends, family members and legal representatives”, citing access to mobile phones and landline telephones.

The Home Secretary said that anyone considered for relocation to Rwanda will be able to access healthcare, welfare services and legal advice, with support and information provided to those “who are in scope for relocation to Rwanda”.

She told the panel: “Nobody will be removed if it is unsafe or inappropriate to do so.”

But the response failed to meet concerns of the IAPDC, which will write again this week to the new Home Secretary.

Ms Lyon told PA news agency: “The panel believes that outstanding concerns remain about taking adequate steps to protect lives.”

A spokesperson for the panel said that the first letter to the Home Secretary came following an observation visit to the Manston immigration centre in Kent.

It will now write another letter to the next Home Secretary, in a bid to get more information.

The spokesperson said: “On September 6, the IAPDC will issue a second request for formal clarification.

“This will seek a response to specific questions raised in the panel’s first letter which remain unanswered.”

The panel, the spokesperson said, will ask again about what form of assessment will be used to determine which asylum seekers are processed in Rwanda and whether it would take health and vulnerability into account.

Questions over whether people would indeed be screened for worsening physical and mental health conditions will also be asked again after being left unanswered, while the watchdog will also ask again if “risk of suicide and self-harm” will be taken into account by officials.

A Home Office spokesperson told PA news agency: “Our world-leading Migration and Economic Development Partnership will see those arriving via dangerous, illegal and unnecessary routes to the UK relocated to Rwanda, where they will have the opportunity to rebuild their lives.

“The dignity and welfare of those in immigration detention is of the utmost importance and we have established policies, procedures and trained professionals in place at every Immigration Removal Centre to safeguard individuals, and support their physical and mental health.

“Rwanda is fundamentally a safe and secure country and no-one will be relocated if it is unsafe or inappropriate for them.”

It comes as the Home Office this week said it had appointed an independent panel to oversee the plan to send migrants to Rwanda made up of eight “experts” in areas including human rights and asylum.