Six inmates were mistakenly freed from prison under the government’s temporary release scheme to combat the spread of the coronavirus, it has emerged, prompting an urgent suspension of the programme. The inmates were wrongly let out of two open category D prisons – Leyhill in Gloucestershire and Sudbury in Derbyshire – along with another from the Isis category C prison and young offenders institute in south-east London. The Ministry of Justice said the men “returned compliantly”. The Prison Service announced earlier this month that it would temporarily release up to 4,000 low-risk inmates who were within two months of their release date on electronic tags following a safety assessment. The scheme, designed to avoid thousands of inmates becoming infected, was paused on Thursday and is due to resume next week. The Prison Service blamed the mistaken releases on human error and said processes would be strengthened. A spokesman said: “We are aware of a small number of low-risk offenders who were released from prison under the temporary early release scheme following an administrative error. The men were released too early but were otherwise eligible under the scheme, and returned compliantly to prison when asked to do so. “We have strengthened the administrative processes around the scheme to make sure this does not happen again.” The shadow justice secretary, David Lammy, said: “It is deeply troubling that out of the handful of inmates released so far as part of the government’s new scheme responding to Covid-19, six were released in error. The mistakes made must be quickly understood and remedied. “These errors must not be used as an excuse for inaction in the face on an oncoming public health disaster. Prisons are overcrowded, with thousands of cells containing more than one inmate, against the advice of Public Health England. “If the Ministry of Justice does not take sufficient steps to move towards single cell occupancy, it is not only inmates and prison officers who will be put at risk. NHS hospitals will become overwhelmed and the virus will spread rapidly from prisons across the wider public.” The revelation comes after two of the country’s biggest penal reform charities launched legal action against the justice secretary, claiming measures taken so far to address coronavirus behind bars are unlawful because they will have a “manifestly insufficient impact”. Lawyers acting for the Howard League for Penal Reform and the Prison Reform Trust wrote to Robert Buckland on Friday with details of a proposed application for judicial review, should urgent action not be taken to address their concerns. The letter said “the rate of releases has been too slow and too limited to make any substantial difference to the prison population and the plans as we understand them are incapable of achieving what the secretary of state has publicly acknowledged is required”. The Prisoners’ Advice Service has also threatened legal action against the government unless vulnerable and elderly prisoners are immediately released to protect them from contracting Covid-19. Coronavirus cases have been confirmed in more than half of the prisons in England and Wales. A total of 255 prisoners had tested positive for Covid-19 in 62 jails as of 5pm on Thursday, the MoJ said, and 13 were known to have died. A total of 138 prison staff have also contracted the virus in 49 prisons, as well as seven prisoner escort and custody services staff.