The family of Allan Marshall, who died after being restrained by staff at Saughton Prison Edinburgh, are to sue the Scottish Prison Service over his death, it has been revealed.

Relatives of Mr Marshall, who died of a brain injury following a cardiac arrest at the age of 30, are also to bring compensation cases against both Police Scotland and the Lord Advocate.

A post mortem found he had a pre-existing heart condition, but a fatal accident inquiry headed by Sheriff Gordon Liddle concluded the restraint had contributed to his death.

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Mr Marshall, who ran a recycling business, was on remand in relation to a breach of the peace charge and as a result of unpaid fines. However on March 28th 2015, after being segregated by officers, he was restrained in an incident captured on prison CCTV footage which was leaked to the Sunday Mail.

This appeared to show him being dragged naked by across a cell floor by prison staff who also used their feet to restrain him.

Following an investigation, the Crown Office decided not to bring criminal proceedings against those involved.

But in his FAI report on the incident Sheriff Gordon Liddle criticised SPS officers and described Mr Marshall's death as "entirely preventable," adding that he had found the evidence of officers involved as "mutually and consistently dishonest."

Yesterday, the newspaper reported that the legal claims follow a review of the case by an unnamed human rights expert.

As well as a civil action against the SPS over alleged failings in its duty of care to Mr Marshall, his relatives - including his brothers Alistair and Jamie, and his aunt Sharon MacFadyen – are understood to be pursuing a claim against Police Scotland, who they believe failed to carry out an adequate investigation into the circumstances of his death, and the Lord Advocate, in relation to the decision by the Crown Office to protect prison staff from prosecution.

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The family's lawyer Jelina Berlow Rahman said: "Sheriff Liddle's report and recommendations found Allan Marshall's death entirely preventable and that the system was defective in that it placed responsibility in the hands of prison officers to make decisions that they were not capable of or equipped to make.

"Police Scotland and the Crown Office and procurator Fiscal Service were partly responsible for the investigation of the death.

"It was the Lord Advocate who granted immunity and this, arguably, was a further deficiency in the investigation."