Criminal gangs are using dead rats to smuggle contraband material such as drugs and mobile phones into jail, the Prison Service has said.

Staff at HMP Guys Marsh in Dorset discovered three rodents that had been stitched up across their stomachs. Subsequent investigation revealed the animals had been stuffed with phones and chargers, sim cards and drugs.

The animals were found just inside of the perimeter fence of the category C institution, which has been plagued by ill discipline.

The Ministry of Justice said the animals had been thrown over the fence of the prison by criminals who had alerted inmates to pick them up.

Previously, gangs have used pigeons and tennis balls to attempt to bypass prison security measures.

The prisons minister, Rory Stewart, said: “This find shows the extraordinary lengths to which criminals will go to smuggle drugs into prison, and underlines why our work to improve security is so important. Drugs and mobile phones behind bars put prisoners, prison officers and the public at risk.

“By toughening security and searching, we can ensure prisons are places of rehabilitation that will prevent further reoffending and keep the public safe.”

The use of the synthetic drug spice has been identified as one of the key problems in Britain’s prisons. Intended to mimic the effects of cannabis, it has been described as the “most severe public health issue we have faced in decades” by Marc Jones, Lincolnshire’s police and crime commissioner.

One of the rats before being opened. Photograph: Ministry of Justice/PA

Drugs found stuffed inside the animal. Photograph: Ministry of Justice/PA

In the 12 months to March 2018, there were 13,119 incidents where drugs were found in prisons in England and Wales – a rise of 23% on the previous year. The prevalence of mobile phones has also increased – up by 15% to 10,643 instances in 2017-18.

Guys Marsh has had a troubled recent history. In 2017 there was a rooftop protest involving a drunk prisoner who set fire to the roof after stripping off and torching his clothes. The previous year, photographs emerged on Facebook showing prisoners drinking, using drugs and eating takeaway fish and chips.

Last year the prison’s independent monitoring board reported that prisoners had easy access to mobile phones and could “make calls at times to suit themselves”.

In 2017, a report from HM Inspectorate of Prisons detailed how inmates were able to walk around the jail in dressing gowns or shorts.

The Guardian reported in 2017 that levels of bullying and violence were so high one of the wings was made into a permanent sanctuary for prisoners fearing for their safety.