The number of prisoners released by mistake has reached the highest level for six years.
Sixty-five convicted criminals or suspects were freed in error in 2015/16 - an increase of 16 compared with the previous year and the highest in any financial year since 2009/10, when there were 68.
An inmate is classed as having been released in error if they are wrongly discharged from an establishment or court when they should have remained in custody and when they had no intention to escape.
The Ministry of Justice said examples can include misplaced warrants for imprisonment or remand, recall notices not acted upon, sentence "miscalculation" or "discharging the wrong person on escort".
Figures obtained by the Press Association last year showed that prisoners in custody for murder and other violent offences were among hundreds mistakenly released in a decade.
It came as a rash of official data sparked fresh concerns about safety in prisons in England and Wales.
It was disclosed that assaults on prison staff have reached the highest level on record - with 15 attacks now taking place every day.
In the year to the end of March there were 5,423 assaults on officers - up 40% on the previous year. The tally included 646 serious incidents.
The overall assault count was up by almost a third to more than 22,000, while in the 12 months to the end of June there were 105 apparent self-inflicted deaths - up from 82 in the previous 12 months.
The figures come days after chief inspector of prisons Peter Clarke warned that too many prisons have become "unacceptably violent and dangerous places".
As the Government published multiple reports, it was also disclosed that:
:: As of the end of last month, 1,341 offenders freed on licence and then recalled to custody after breaching the conditions of their release were still at large, including 177 who were originally serving a sentence for violence and 42 for sex crimes. The figures include some individuals believed to be dead or living abroad, the MoJ said.
:: The overall performance of six prisons was rated as being of "serious concern".
:: One in four adult or juvenile offenders committed a new offence within a year of being cautioned, convicted, or released from custody. The re-offending rate of 25.7% is a slight fall on the previous 12 months.
:: In 2015/16, 24.5% of prisoners were held in "crowded" conditions, a decrease of 1.0 percentage points from 2014/15.
Andrew Neilson, of the Howard League for Penal Reform, said: "Prisons are not only becoming more dangerous, they are becoming more dangerous more quickly.
"That more prisons have been awarded the worst-possible performance rating provides further indication of how the system is failing after years of rising numbers, chronic overcrowding and deep staff cuts."
Justice Secretary Liz Truss said the level of violence in prisons is "unacceptable".
She added: "I am clear that safety in prisons is fundamental to the proper functioning of our justice system and a vital part of our reform plans.
"There are a number of factors, including the availability of psychoactive substances in prisons, which must be tackled.
"It will take time to address these long-standing problems. I am determined to make sure our prisons are safe and places of rehabilitation."