Teresa Medhurst said the SPS should be at risk of criminal prosecution over deaths in custody.

She made the comment in a meeting with the families of Katie Allan and William Brown, also known as William Lindsay, both of whom died by suicide at Polmont Young Offender’s Institution in 2018.

Crown immunity means that government and official bodies, such as the prison service, may be protected from being charged with criminal offences that have been created by statute.

It does not always protects prison officers or officials though, such as in situations where they are caught using, possessing or giving a “personal communication device”, like a mobile phone, to a prisoner.

The Scottish government said it is seeking a change in the law but that it would require UK government approval.

Ms Allan’s mother, Linda, said the meeting was “very positive”, and that it was the “beginning of a dialogue” with the SPS.

She said: “For the first time we didn’t feel demonised by the prison service, but we felt listened to, and we found that very restorative.”

Ms Medhurst said: “This was just an opportunity to meet personally with the families, to offer our apologies for their loss, the tragic loss of Katie and William, and to apologise for the failures of the past.

“And to ensure that they understand we are committed and determined to not only action the recommendations that we have accepted in full, but to ensure that there is systemic change across the organisation, which will be impactful and lasting.”

A spokesperson for the Ministry of Justice said: “The lord chancellor has received the letter from the Scottish cabinet secretary for justice and home affairs and will respond in due course.”

A Scottish government spokesperson added: “The Scottish government will continue to pursue the lifting of the SPS corporate Crown immunity under reserved health and safety law with the UK government.

“All of the recommendations in his determination of the FAI into the deaths at Polmont YOI of Katie and William have been accepted and the work on these is being delivered at pace with progress closely monitored.”