Prisoners at HMP Peterborough were given an extra 900 days in jail last year for breaking prison rules.
The total is up on the 681 additional days in 2014 at the Sodexo-run prison in Saville Road, Westwood,
The prison’s average population last year was 1,188.
In total, more than 17,000 days – or 48 years – of additional imprisonment were imposed on prisoners found to have broken the rules in prisons in the East Anglia region last year.
The figures are revealed in a report by the Howard League for Penal Reform.
The report, called ‘A Million Days: The world of prison discipline’ states that more than one million additional days – equal to almost 3,000 years – have been imposed on prisoners since 2010.
The report looks at how prisons operate disciplinary hearings called adjudications, where allegations of rule-breaking are tried. These mainly concern disobedience, disrespect or property offences, which increase as conditions in prisons deteriorate.
Ministry of Justice (MoJ) data show that, across England and Wales, the number of additional days’ imprisonment imposed has increased by 30 per cent in a year – from 165,856 in 2014 to 215,348 in 2015.
Private prisons generally hand down more additional days of imprisonment per prisoner than public prisons. Of the 14 private prisons in England and Wales, all but two imposed more additional days in 2015 than in 2014.
The report marks the start of a new Howard League campaign to reduce the number of people in prison by reforming The 3Rs – rules in prison, release from prison, and recall to prison.
The campaign aims to get immediate behaviour change by authorities that would ease the pressure on the prison estate by reducing the population.
The campaign begins in the week when up to 10,000 prison officers stopped working during a day of protest at what they say is the intolerable conditions behind bars.
Frances Crook, chief executive of the Howard League for Penal Reform, said: “The system of adjudications has become a monster. Originally intended as a way to punish incidents of unacceptable conduct, it is now routinely used as a behaviour management technique by prisons that are out of control.
“Instead of solving the problems, these punishments feed a vicious cycle, piling more pressure on the prison population and worsening overcrowding, which in turn creates conditions for drug abuse and violence.
“At the same time, rules to incentivise prisoners’ behaviour have been made more punitive, which is also contributing to the poisonous atmosphere behind bars.
“The government has acknowledged that there are problems in the system, but warm words are not enough. The imposition of additional days should be seen as a sign of a poorly performing prison and included in new measures being proposed to monitor safety and order. The rules around incentives and earned privileges must also be revised, as ministers have now promised.
“The Howard League 3R campaign will ask governors to deal with infractions instead of referring to external adjudicators, and the judges to exercise self-restraint by not bloating prison numbers even more.”
Governors have a choice in the way they deal with rule-breaking. They can manage it themselves or pay for an external adjudicator (a district judge) who has the power to impose additional days of imprisonment.
The number of cases sent to external adjudicators soared by more than 80 per cent between 2010 and 2015.
The report states that new guidance, issued by the Chief Magistrate in 2015, to impose more severe punishments for rule-breaking has contributed to an “explosion” of additional imprisonment.
The Howard League estimates that the extra days imposed in 2015 has cost the taxpayer £19 million on top of what has been spent on running the adjudications.