The Supreme Court has rejected a bid to have a deputy coroner removed from an Aboriginal death in custody inquest.

In 2016, Wayne Fella Morrison died in the Royal Adelaide Hospital, three days after being found unresponsive in a prison transport van at Yatala Labour Prison.

Eighteen South Australian prison guards and a nurse at the centre of a coronial investigation into the death in custody attempted to have the deputy coroner thrown off the inquest this week.

They lost the bid, but the ruling prevents deputy coroner Jayne Basheer from compelling them to answer questions about the man’s death.

Mr Morrison was handcuffed and placed in ankle flexi-cuffs and a spit mask, face down in the rear of the van, with eight prison officers accompanying him.

It has been alleged that Mr Morrison became violent in the holding cells before his bail hearing and assaulted several prison officers.

Eighteen prison guards and a nurse asked the Supreme Court whether Ms Basheer could force them to give evidence at the inquest into the death.

Of the 19 witnesses, seven have already given evidence, four are part-way through and eight have not spoken yet.

Lawyers for the prison guards have previously argued that they should be able to exercise privilege against self-exposure to a penalty and against self-incrimination.

They also allege that the Coroner's Court was not entitled to look at what happened after Mr Morrison was pulled from the van.

They accused Ms Basheer of “apprehended bias”, due to her previous association with the Correctional Officers Legal Fund and a law firm at the heart of the inquest.

The deputy coroner has rejected those arguments, saying the question of self-incrimination can be dealt with on a case-by-case basis.

She pointed out that coronial inquests are not bound by the rules of evidence in the same way as other court proceedings.

Lawyers then appealed Ms Basheer's decision in the South Australian Supreme Court, which has found “no reasonable apprehension of bias”.

“There is no basis on which a fair-minded lay observer might apprehend that the coroner might not bring an impartial mind to the resolution of the question she is required to decide by reason of pre-judgment,” Justice Malcolm Blue found.

He said Ms Basheer had “no obligation” to disclose her association with the Correctional Officers Legal Fund in 2010 and 2011.

“The fact that the [deputy] coroner did not make that disclosure does not carry evidentiary weight in the circumstances in relation to the question of reasonable apprehension of bias,” he said.

The inquest has revealed that some prison guards did not complete incident reports.

Justice Blue found the deputy coroner could not rule on misconduct or recommend disciplinary action in her final recommendations against the officers that did not complete incident reports.

“The substantial majority of correctional officers did provide incident reports, including the van officers,” he said.

“In general, those who did not provide incident reports tended not to have participated in the incidents that occurred on that day and were merely observers.”

Justice Blue also overturned an order made by Ms Basheer preventing the guards from refusing to answer questions or present documents.

The inquest is set to continue on slightly modified terms.