Police chiefs have told ministers they fear that the crisis gripping the Prison Service in England and Wales is “unsustainable” and risks public safety, the Guardian has learned. Government and prison chiefs have taken a series of crisis measures because of overcrowding, including plans to free convicted criminals early and using police cells to house those who otherwise would be in jail. Sources with knowledge of the discussions between government and senior police leaders, including the chair of the National Police Chiefs’ Council (NPCC), Gavin Stephens, confirmed the dire warning had been given to ministers and senior officials in recent days. Senior police figures believe the use of their cells cannot go on, with the Prison Service paying to use them because of severe overcrowding. They have also been asked to consider delaying some operations that would lead to arrests to ease overcrowding, in advice issued by the NPCC. In addition, they have been asked to consider whether arrests can be delayed for non-priority cases, as long as the public are not placed in danger, according to documents first reported by the Times. One source said this would cover arrests where police could safely delay a raid for some time, or detaining multiple suspects, but not a case where someone is arrested immediately after committing a crime. Multiple sources confirmed the documents are genuine and accurately spell out the level of concern within policing. The document sent to police chiefs by the NPCC says: “Consideration is to be given to pausing non-priority arrests and any planned operations where large numbers of arrests may take place to ease the pressure within the criminal justice system. “Notwithstanding public protection remains a priority and a considered threat, harm and risk assessment is to be completed when considering any pause in police operations.” Shabana Mahmood MP, the shadow justice secretary, committed the Labour party to building new prisons, saying: “It beggars belief that police are being told to sit on their hands and ignore crime because the Conservatives have mismanaged the criminal justice system so badly. “Rishi Sunak’s rap sheet now reads: the rushed early release of domestic abusers on to our streets, deliberate delays to trials, and victims waiting years for justice. The public will be absolutely dumbfounded. This cannot go on. “Labour is the party of law and order. We will build the new prisons needed and make Britain’s streets safe.” Later this week, the Ministry of Justice is expected to start the early release of some inmates 70 days before their incarceration is due to end. Earlier this month the Guardian revealed the escalating prison crisis and that the government had triggered Operation Safeguard, where those who would normally be in prison are sent to police cells instead. At the start of May, the prison population in England and Wales was 87,505, with the official usable capacity put at 88,895. Capacity has increased by 3,000 places in a year, but still cannot keep up with demand. Operation Safeguard is meant as a temporary measure and is an expensive choice to house inmates who have either been convicted or who are on remand awaiting trial. Cuts to prison budgets have left the system in crisis, leading not just to overcrowding but damning reports from independent inspectors warning of dire conditions.