The discovery of a suspected explosive device led to parts of a prison being put on lockdown on Sunday, the Guardian understands.
The incident inside HMP Risley in Warrington is not being treated as terror-related and has been referred to the police.
A Prison Service spokesperson said There was an incident at HMP Risley on Sunday 12 November. There was no threat to the public or those within the prison. The matter has been referred to the police and it would be inappropriate to comment further.
The category C prison in Cheshire, known locally as Grisly Risley, holds about 1,115 adult men, mainly from the north-west, serving short and intermediate sentences.
In 2016, Pia Sinha, a psychologist, was announced as governor of HMP Risley, becoming one of the few women to run a UK prison.
That year, prison inspectors identified a number of failings at the institution, including poor hygiene and safety concerns.
Last month, the Ministry of Justice announced prison officers at HMP Risley would trial the use of incapacitant spray, which is similar to pepper spray, for dealing with violent offenders.
In October 2016, Renelle Carlisle, 23, was jailed for three years and four months after he was caught outside Risley with a drone in his bag, trying to smuggle drugs into the prison.
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