Frontline prison officer numbers have fallen by more than a quarter in six and a half years, figures reveal.
At the end of September there were 18,003 staff across three key categories in public sector jails, a dip of 87 (0.5%) on the previous quarter and 417 (2.3%) over the last 12 months.
When structural changes are excluded, there has been a reduction of 6,335 personnel classed as "full-time equivalent" since March 2010 - or a 26% fall.
The numbers relate to band 3 to 5 staff, which are the key operational grades in public prisons and consist of officers, specialists, supervising officers and custodial managers.
A report published on Thursday by the Ministry of Justice said the overall shortfall of officers in the bands against benchmark or target staffing levels was 800 (4.3%) at the end of September.
There has been close scrutiny of prisons in England and Wales in recent days after the escape of two inmates from HMP Pentonville in north London.
The Prison Officers Association has claimed the breakout followed years of under-investment and staff cuts.
Rising levels of violence and self-harm behind bars have also led to a string of warnings about the estate.
Last week Justice Secretary Liz Truss unveiled a package of measures aimed at reforming prisons, including a recruitment drive to add thousands of new officers to the front line.
A Ministry of Justice spokeswoman said: "We are committed to transforming prisons into places of safety and reform and we've announced a major overhaul of the prison system including 2,500 extra frontline officers.
"As an immediate action we have already invested £14 million to provide more than 400 extra staff in 10 of the most challenging prisons.
"We are also introducing a new scheme to attract top graduates and former servicemen and women into the service, and giving governors greater flexibility over recruitment so they can address staffing quickly."