The ease with which a prisoner obtained illegal drugs was a factor in his death, an ombudsman report has said.
John-Paul Pace, 41, was found unresponsive at HMP Chelmsford in 2020 after having taken the psychoactive drug spice.
The Prisons and Probation Ombudsman said managers needed to prevent supply and demand of illicit substances.
A prison service spokeswoman said: “We have invested £100m into tough security measures… to block more contraband.”
The officer who found Mr Pace in his cell on 22 July 2020 did not call for clinical assistance upon finding him and failed to make the appropriate emergency call immediately, the ombudsman’s report said.
Instead, she fetched a senior officer, going down two flights of stairs and through two locked gates, before the emergency “code blue” radio call was made.
Mr Pace had died a few hours before he was discovered.
The officer had been seconded to Chelmsford in January that year and so had not taken part in mandatory training for emergency procedures, the report said.
Mr Pace was described as “friendly” by staff and the prisoner in the neighbouring cell said he appeared “perfectly normal” before his death.
He had a history of drug misuse, but on 28 May had withdrawn from a drug treatment programme against medical advice.
The ombudsman Sue McAllister said: “I am concerned that Mr Pace was able to obtain illicit drugs at Chelmsford with apparent ease.
“The prison needs to continue its efforts to prevent the supply of and demand for illicit substances.”
She said the prison had since taken active steps to reduce the supply of drugs, including using a Rapiscan machine, to detect drugs in mailed items.
The delay in calling for help “concerned” her because while it would not have changed Mr Pace’s outcome, “it could be crucial in future cases”.
An HM Prison Service spokeswoman said: “Our thoughts remain with Mr Pace’s family and friends.
“We have invested £100m into tough security measures across the estate to block more contraband entering our jails, and continue to work to wipe out all illicit drugs in prisons.”
An inquest at Essex coroner’s court, held in October, concluded Mr Pace’s death was drug-related.