The prisons ombudsman, Adrian Usher, sent his condolences to those affected.

After initial enquiries, Mr Usher said he now believes at least four of the deaths at HMP Parc in Bridgend were "drug-related".

He said the deaths "likely" involved spice, mixed with another family of drugs.

"There has been a national public health warning issued about this particular drug, the name of which is yet to be determined, but we believe that at least two of the deceased at HMP Parc had taken this substance," he said.

"It is therefore likely the deaths are all spice-related."

The prisons and probation ombudsman has urged all prisoners in possession of spice to "dispose of it immediately".

"This is a dangerous drug and we do not want to see any more unnecessary deaths occur," Mr Usher added.

"Friends, family, next of kin, and staff in prison - please share this message as wide and as quickly as possible".

Opened in 1997, HMP Parc is a category B men's private prison and young offenders institution.

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Sky News understands 20 deaths at HMP Parc were reported to the ombudsman from 1 January 2022 to 20 March 2024.

Six of these were reported to the ombudsman in the last three weeks.

Sky News has contacted G4S, which manages HMP Parc, for comment.