An inside source told a prison phone service that they heard cockroaches moving around in their cells at night resembling “the size of mice.”

An Islington prison has been found to have a widespread cockroach infestation just a week after a damning report into the “squalid” conditions suffered by inmates.

HMP Pentonville, on Caledonian Road, Holloway, was found to have “filthy” prison cells with “accumulated waste”, “mounds of rubbish” and blood stains on the walls and beds and a build up of human excrement in the toliets, a report by the prisons’ inspectorate at the end of June revealed.

Despite high numbers of complaints by inmates, the prison management response was described as “cursory” and “did not fully address the issues raised.”

Nick Hardwick, HM Chief Inspector of Prisons, also noted the high number of violent incidents in the prison and many of the inmates testing positive for illegal drug use, as well as widespread overcrowding.

The report condemned the often severe understaffing of the category B prison for men, and the lack of engagement of prison staff with inmates and opportunities for inmates to learn the skills necesssary for rehabilitation.

Mr Hardwick issued a clear warning that the prison needed “a firmer grip” and “a persuasive plan that will ensure immediate...improvements” to determine whether HMP Pentonville “had a future.”

But an anonymous source has since revealed to prison phone service Prison Phone that they have heard cockroaches moving around in their cells at night and have seen many resembling “the size of mice.”

This latest allegation of a cockroach infestation in HMP Pentonville has angered penal charities and reformers.

Prison Phone accounts manager Claire Jones said: “When faced with bleak surroundings such as this, it’s hardly surprising that inmates struggle to focus on rehabilitation.

“How exactly is a prisoner meant to focus on becoming an integrated member of society in the future when they are being treated as an animal?”

Frances Cook, chief executive for the Howard League for Penal Reform, agreed: “Pentonville is old, but do not blame the building. It is what we do with it that matters. When a prison is asked to hold 350 more prisoners than it is designed for, we should not be surprised when it fails.”

The Ministry of Justice did not respond to a request for comment.