Justice Secretary Kenneth Clarke was warned about staffing concerns at an open prison a fortnight before inmates went on the rampage, it has emerged.
The local Independent Monitoring Board – a group of volunteers who carry out checks – also warned about alcohol being smuggled into Ford open prison.
Some 40 inmates rioted at the jail in West Sussex on New Year’s Day after officers attempted to breathalyse them.
The Ministry of Justice said it would consider the report’s findings.
At the start of the riot, which is estimated to have caused £3m worth of damage, two officers and four support staff on the night shift were in charge of almost 500 prisoners.
In a report from 16 December which has now been published, Ford’s Independent Monitoring Board said it had concerns about “minimal” staffing, as well as junior staff – who were only trained to a low level – patrolling alone.
“Whilst there have only been minor incidents in the last year, we do not consider that proper control is being exercised at night and are sceptical of the response received in the past that it must be adequate because there has not been a serious incident yet,” it said.
It went on to warn “drugs, alcohol, mobile telephones and other illicit substances” continued to find their way into the prison.
The report echoes concerns about low staffing levels from the Prison Officers Association.
Last week the POA said only 43 prison staff are in charge of more than 3,000 inmates on a typical night shift at open jails.
Joe Simpson, of the POA, said the numbers were “totally inadequate” and he was surprised recent unrest at an open prison had not happened sooner.
Earlier this week Mr Clarke told the Commons that lessons must be learned about what happened at Ford.
The National Offender Management Service is carrying out an investigation.
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